Don't remember much about Pro Street, I didn't give that game much of a chance for whatever reason (I should try it again soon), but this game has some occasional slowdown in various places. Doesn't really detract from the fun the game provides me though as it's not too extreme. Looks like it's essentially 30FPS.
I'll tell ya, this is the most fun I've had with a DS racing game since Speed Racer. One thing I really like is that you don't have to muck about with tweaking car settings if you don't want to, just race. I like that. Some of the NFS games were annoying with all that forced customization crap to stay competitive. I just want to race, not piddle with settings. It's one of the things that annoys me about Smackdown 2010.....all the boring training mini-game blah over and over again made me lose interest. But I digress.
Something I realized late last night; you're supposed to hit all that breakable stuff (cones, barricades, trees, lamp posts, etc.) while racing to crank up your score. Kinda counter intuitive for me in a racing game, you know?