Powerslide should definitely be silky smooth at all times, just like it used to be, but I was experiencing frequent noticeable drops in frame-rate in 3Dfx mode.

I found that configuring nGlide and setting "Vertical synchronisation" to "Off" fixed the problem (with no apparent ill effects).

Failing anything else, you can always play in software mode :) I was slightly astonished to see that the game offered and ran at 1920x1080 (but sadly not at a sufficiently playable frame rate).