The question of Sonic's top speed is seemingly unanswerable. There are, of course, also the light-speed shoes to consider. We might also reference the manual for Sonic Adventure DX, which boasts a top speed of 3,840 miles per hour. If we allow ourselves to suspend our disbelief, we could trust Sonic Unleaded's in-game speed meters, which have clocked Sonic at up to 2,500 miles per hour.
If Sonic were truly zipping around faster than the speed of sound, it would have a pretty detrimental effect on gameplay. To be fair, these calculations stuck strictly to what can be seen during gameplay and that is, understandably, restricted in order to make the game playable. The word 'sonic' is in his name, after all. That's a far cry from the bill of goods we've all been sold. According to their calculations, the Blue Bolt clocks in at just about 80 feet per second, on his best day.
