The PSP can do a lot of things! The PSP can do things over wi-fi. The PSP can now run at 333mhz. Both good things. Problem is, it can't do both of them at the same time. Beyond3D have found that a game can only run at top-speed if the PSP's wi-fi is disabled. If it's not, the fastest a game can run is a good old-fashioned 222mhz. David "Davey" Karraker has confirmed this with GameDaily, saying:
The article is correct that increased CPU speed cannot be used with the PSP's wireless feature.
No confirmation on just why the limitation is in place, but I'd think the 34-second battery life you'd get with both features running may have something to do with it. Sony PlayStation Portable: 333MHz comes with restrictions [Beyond3D, via GameDaily.biz]