Option to underclock PSP?

[VIRGIN KLM]

Soul Calibur and Tekken series are heavily GPU orientated here.
I can easily get 60 VPS (and rather jerky gameplay) with frameskip and 1.5GHz CPU.
Remove frameskip and I'm getting about 20 FPS.

Sure, 1.5GHz is a lot. But my GPU ain't bad either.

I think lowering the 333MHz clock to 222MHz in Tekken will have the adverse effect. It will choke the game and slow it down further.

Have you tried it? Because it doesn't, even at lower values than 222MHz.
Don't think of them like how they react to underclock settings/speedhacks in PCSX2 (speedhack is working as a slowdown instead of a speedhack).