I was playing Pulse today on my train ride!
It's not 60fps, and isn't constant, dipping all the time on certain tracks. But it's certainly above the 30fps of the PSP original running on standard handheld. When the frame rate is solid, it's a lovely sight to behold, and smoother in action than 2048. And I hated the nub on the PSP, so always played games with the d-pad. Finally being able to use analogue controls for Wipeout is a massive bonus.
What I've found with PSP games running on Vita is the performance is the same as on a PSP running custom firmware that allows you to increase the CPU clock speed from 266MHz to 333MHz. This would give performance boost to loads of games. Sometimes minor, sometimes pretty noticeable.