Quick aside here:

There's a lot of speculation that Sony will reveal an updated PSP model at next month's E3 conference. The feeling is that 333Mhz takes such a load on the PSP battery that Sony must have plans for a hardware revision in place for the arrival of games that actually are programmed for the 333Mhz speed.

Supposedly, games that aren't programmed to use the faster speeds shouldn't actually be affected by the updated firmware. (Not that I have tested this myself or anything )