=> Ape Escape appears to run fullspeed but as soon as you press Start in-game the Options menu will cause slowdown. Gran Turismo 2 (Arcade) will slowdown as soon as you enter a race. Spyro 3 also suffers from slowdown.
interestingly, i am unable to recreate slowdown in these two scenarios on my pi4 + aarch64 + kms + latest mesa drivers setup
on my stock (albeit updated) pi4 + arm32 setup i couldn't recreate slowdown in ape escape's menu (only tried the tutorial level, though), but i could get it in GT2 (just X'd through the menus to get to the first race).
i tried fkms (ie, retropie/raspi pi os's default) on my aarch64 setup: still no slowdown. i don't think aarch64 should make a difference since this a GPU bottleneck. it could be the latest mesa drivers (which allegedly have some performance improvements).
anyway, i will default it on software for now but this might be something we can review when raspi os is updated.