Not every game ever, but all PAL titles and a quite a bunch of japanese ones. Has to be over 400 titles for sure.
Not counting Deinterlacing, the only title that was running slow was Astal, and only because it needed the SH2 Cache option to boot. (but only at boot, so you could make a savestate of the title screen and run it full speed without that option)
SSF is heavily multithreaded by the way, you can fiddle around with the thread options to make it use more cores better. The defaults work fine on my machine though.
I definitely recall some slowdown, freezing and still a few titles it wouldn't boot at all. That's on a Core i7 with 16GB of RAM.
I've found that most discs containing multiple titles won't boot, such as (most of) the Sega Flash demo series and Die Hard Trilogy. However, Sonic Jam and Capcom Generations* plus the Atari and MSX collections seem to work fine. As for hardware specifications, if 16GB of RAM and a Core i7 isn't enough to get SSF running perfect there really is no hope!
*Actually, the compatibility notes I've created include a brief note about this one throwing up occasional SH2-based emulation errors.
Just bump up the compatibility mode. Sega Flash works fine. There's a small graphical glitch with the graphics not lining up with the background and thats all.
They used to crap up because the emulator couldn't handle the multi-disc loader Sega sample code. Note that every game you load in Sega Flash starts from the Sega boot logo - they are not run as a piece of game data, instead they are loaded like as if you'd boot a disc from the start. Sonic Jam, Capcom Generations, Atari and MSX compilations don't load entire external games from a subfolder, they just load one tiny piece of their own main code.
Die Hard Trilogy hangs up before it could even boot the game selector, it's an entirely different thing.