Great topic!
I'd say the fastest coaster I've ridden feels like Oblivion at Alton Towers. I don't know if the tunnel causes an enhanced sense of speed or something, but this feels seriously fast, even though I've ridden a few faster coasters. Honourable mentions go to Stealth at Thorpe Park (which is the fastest coaster I've ridden; on the front row in particular, you can really feel its speed!), Silver Star at Europa Park (my front row ride on this felt ridiculously fast! Also the 2nd fastest coaster I've ridden; Stealth and SS do feel as fast as their billed speeds, in my view!), Wodan Timbur Coaster at Europa Park (this is just relentless!) and The Swarm at Thorpe Park (this feels obscenely fast, particularly as you're plummeting down the first drop and hurtling out of the zero-g roll!).
In terms of coasters that feel a lot faster than their perceived speed; I think that both of the GCI coasters I've done are very good at this, so Wodan gets thrown into the ring once again, but I think Wicker Man at Alton Towers is a better candidate for this category out of the GCIs; WM supposedly goes 18mph slower than Wodan, but it doesn't feel far off Wodan's speed in sections! I also think Space Mountain Alpha at Magic Kingdom feels a fair bit faster than 28mph. Also, let me mention Runaway Mine Train at Alton Towers; how that helix into the tunnel feels so fast when the ride goes only 22mph well and truly defies physics!
As I've seen a few people talk about coasters that don't feel as fast as they supposedly are; one that comes to mind for me in that category is Blue Fire at Europa Park. As much as I don't think that it's a slow ride by any stretch, and does feel fast, I also don't think that The Big One at Blackpool Pleasure Beach feels quite as fast as many coasters that are slower than it, particularly once you pass the first drop (which I'll admit does feel pretty fast!). I think I could also make an argument for Thirteen at Alton Towers possibly not feeling as fast as 42mph compared to other coasters I've done that are slower. It certainly feels like it and Wicker Man have a far greater speed difference than a mere 2mph, although that's probably more a testament to Wicker Man's blisteringly fast pacing than Thirteen being even vaguely slow!
EDIT: One I forgot to mention; I'd argue that Grand National at Blackpool Pleasure Beach also feels faster than 35mph! And in a possibly controversial one, I'd argue that Megafobia at Oakwood feels slower than it is.