There are many that wonder why Sonic and co. are rated lower here in terms of speed then other wikis; I below will explain the following reasons why:
Cyan Wisp
When Sonic first interacts with a Cyan Wisp it envelops his body and makes him move as a laser[1], that's outright stated to move at the speed of light[2], Sonic is completely shocked by the speed he gets when he uses it and it is way faster then anything he can do[3], they even acknowledge the Sonic Colors Ultimate Short Animation that it's far above his speed[4]. Sonic Colors 3DS notes that the cyan laser let's Sonic fly through the air at "blinding speeds" already showcasing it's far above his regular speed[5].
An argument people try to make for why Sonic is comparable to the Cyan Wisp is that he caught up to it and claimed it's almost as fast as him[6]. However, there is missing context to this, prior in the cutscene the wisp is shown in its normal body moving[7], when actually activating the laser there's a flash of light in the same cutscene[8] Tails even notes the flash of light specifically is the power of the Cyan Laser[9] with Sonic even claiming that he wants to see how fast it is[10]. This string of dialogue showcases that the cyan laser itself is not what he caught, but the Cyan Wisp while it was still in its wisp form, which we see in Colors Ultimate that the cyan wisp will run from things without automatically turning into its laser form[11]. Thus Sonic did not catch up with the cyan laser power of the wisp, but just the Cyan Wisp itself.
Official Statements
While many try to use official statements claiming he's the speed of light, these are always used in a hyperbolic sense.
One comes from a Sonic Adventure interview where they note that he zooms all around at light speed[12], but this is in context talking about how large the levels are and how they don't think most players will notice the details as they will be zooming through the levels. They're not saying that you're literally moving through the levels at light speed, this is especially apparent with famous parts of levels such as the orca chase in Emerald Coast[13], the avalanche chase in Ice Cap[14], not running down a large building instantly in Speed Highway[15], getting forcibly pulled into a tornado in Windy Valley[16], the boulder chase in Lost World[17] and more. If one wanted to argue that this statement isn't hyperbolic, this is a developer interview before the game officially released thus these level locales would clearly show they don't actually intend for Sonic to be running through them at light speed.
Another comes from a statement from a Sonic Unleashed guide, where it states his usual self runs around at the speed of light[18], however this is another hyperbolic statement. For one the guidebook is claiming Werehog Sonic is slow, this is only true in gameplay, in actual cutscenes Werehog Sonic is shown[19] to move around fast[20]. On top of that the very game itself also showcases scenes that go against this statement, Sonic and Chip take all day to see if anyone knows who Chip is[21], he notes in cutscene that he can sprint to a neighboring continent if the planet wasn't broken[22], he takes a bit of time to catch up to Eggman whose flying away[23], has to run around a building for a bit rather then instantly[24]. On top of this Sonic Unleashed entire plot is due to the chaos emeralds being drained of their power Sonic must travel to each continent and restore the chaos emeralds power, restoring the continent back[25], something to where if he was as fast as the guide is claiming, wouldn't have even taken multiple days, even if the continents are broken apart. Examples can even be seen in the story,
he starts a day time stage here[26] then another daytime stage in the same area[27] with both of these taking until night time in one city[28].
Another claim is from the Sonic the Hedgehog Super Interactive Annual 2014 where it claims he runs faster than the speed of light and is the fastest video game character of all time according to Guiness Book of Records[29]. To start with, the Guiness statement seems to be a hoax, no matter where one tries to search up this claim there is no actual record currently sourced for it. Secondly, this is another hype statement that comes from a European guidebook, it's a tertiary canon that does not line up with the portrayal of Sonic's speed in the mainline canon. Due to the usage of using a known hoax for the argument and coming from a tertiary canon that's not the main source, this statement is not very usable.
Another statement comes from Takashi Iizuka claiming "We aren't aware how fast Sonic the Hedgehog is. In some games, he is able to go beyond the light barrier. We don't really know, the best way we can say it rivals the famous comic book hero, The Flash.". While this seems clear cut, there is a massive issue. This interview does not exist. If one tries to look it up and use the exact wording as shown in the picture it will only take them back to a singular blog that has a cropped screenshot of it made for the sole purpose of pushing FTL Sonic. Thus this statement is not usable until an actual legitimate source confirms the legitimacy of this interview ever existing.
Light Speed statements are even noted by Ian Flynn to be characters being arrogant and they are not actually able to move at the speed of light[30].
It should also be noted, Eastern media uses speed of light a lot as a method for saying "very fast" rather then literally being the speed of light. It boils down to even doujins using it as a way to claim certain things and one getting home fast.
Omega statement
The Omega statement is a pretty popular one where one attempts to use Omega stating that light speed would be surpassed, though the full context of this is somewhat ignored.
For one, in Sonic Colors DS continuity Sonic doesn't even have boost[31] until the Wisp give it to him[32]. So collecting wisps make him move faster.
Secondly, Omega's statement in context is talking about Sonic's immense growth and how he keeps getting faster and faster each time he's doing the challenge, where if he keeps it up then light speed will eventually be surpassed due to breaking unprecedented growths.
SPD from Unleashed
Many try to use the SPD due to the boost SPD being rated higher then the light speed dash, however the SPD isn't programmed in a lineal way. Along with this it's clear by the context of the game that it's just apart of Ludonarrative Dissonance to get players excited by seeing how high of a value they're going. For note, the light speed dash's SPD isn't even consistent which already poses a problem since light speed is a static number, it doesn't get faster or slower.
Other Speed Issues
There are a couple of plot points in various Sonic games that greatly mess with the idea that Sonic is light speed or even faster than light.
In Sonic Adventure 2 Sonic and Shadow need to escape the island before it blows up[33], both needing actually being worried and needing to hurry out of the forest[34]. The time limit for this stage is 8 whole minutes[35].
In the plot for Team Sonic in Sonic Heroes, they have three days to stop Eggman from his plot[36], with the three levels you do taking two whole days before getting to Casino Park[37] and then by Rail Canyon they only got until sunset[38].
In Sonic the Hedgehog (2006) there are times Sonic has to enter his "super-speed speed[39]" state, where he will not stop running and is going at top speeds[40].