You nearly made me jump out of my chair there!
I'd love to play Secret of Mana on a handheld. But i read it barely works, unfortunately.
And with 200Mhz it appears to be underpowered for most DOSBox games.
The GP2X sounds like an awesome concept, but it appears to be a little underpowered (or rather: lacks optimized emulators). I'm not going to 200Euro to have jerky gameplay with Commander Keen.
The GP2X can overclocked very easily. All units can go up to 240, most to 270 and some to 300. But yup, you are right. It does seem a little under powered. It fails to emulate N64 and PSX emulation is downright nasty right now. This little unit isn't for everybody but it's definitely worth keeping an eye on. The emulation is getting better and better all the time (for instance, breakthroughs in GBA emulation where we now have most games full speed W/O sound).
Of course, Doom, Doom II, Duke Nukem 3D, Desent, and a few other PC games have been ported.
You will find the current status of all emulation here.
btw, just to attempt to round up my 'sales-pitch' the GP2X can play music files, movie files and has inbuilt text and photo apps. Score!