I'm also very happy with my PSP (fullspeed Playstation, Genesis, Sega CD, PC Engine, NES, C64, etc. plus PSP hits like "Dracula X Chronicles" and "Silent Hill Zero").
But now the GP2X Wiz is available which runs by default at 533MHz and can safely be overclocked to at least 700 MHz (even 800 MHz is often possible, depends on the chip).
UAE4All 0.8.0 has just been ported a couple of days ago. Turrican is reported to run fullspeed with sound.
Turrican II and Superfrog need frameskip 1 for "full speed" with sound. But that's still 25fps and very bearable on a handheld.
The Wiz is quite cheap, too, so I'm really considering getting one after all (since the Pandora just refuses to get completed).
So for Amiga 500-emulation, MAME-emulation and those SNES-titles that run crappy on the PSP (like "Super Turrican", "Mega Man 7", "Chrono Trigger", "Super Mario RPG", and quite a few more) the Wiz is currently the best gaming handheld.
(Unless you can jailbreak your new iPhone 3G S - which has the same CPU and GPU as the Pandora will have - and attach gaming controls to it.)