Regarding emulation, the emulator has to run not only the game, but virtual versions of the hardware the game expects to be dealing with (for example, DOSBox has to emulate a CPU, a least one disk drive, memory structure, video card, sound card, input devices, DOS... and
a game). This is why emulators, no matter how well written, are never as fast as direct ports - they have a lot more work to do.
It also doesn't help that a lot of modern systems (console or otherwise) are designed with multiple cores in mind. For example, most games these days rely on a GPU to get a lot of the work done. Emulation of older single-threaded stuff can't easily be split over multiple processors, meaning that a lot of the host machine's system power goes to waste.
What this means is that the PSP is arguably better suited for playing "native" games (two 333mhz processors and a 3D graphics card), while the iPad/Phone should be better suited for emulation (up to around a full 1ghz on a single processor). So, there's definitely hope there if the PSP is handling it.