Your link is broken.
Specs:
GP32:
http://en.wikipedia.org/wiki/GP32#SpecificationsARM 920T, 133MHz (everything - processing, graphics, etc)
8MB RAM
GP2X:
http://en.wikipedia.org/wiki/GP2X#SpecificationsARM 920T, 200MHz (central processing only)
ARM 940T, 200MHz (dedicated to graphics)
64MB SDRAM
64MB NAND Flash ROM
The GP32 has a small list of emulated games due to it's slow processor and limited resources (memory, etc). The GP2X looks to change that by (a) upping processor speed, (b) adding a dedicated graphics processor, offloading all graphics drawing (and MAME blitting) to the new processor (SDL compatible for XMAME under Linux, which the GamePack will use) and (c) adding a bucket of usable memory.
Again, my desire is for CPS2-level games (and less, obviously) to run full speed 60FPS on this new unit. If that works out, I'll be buying one immediately.
Also, it's worth remembering that there are emulators OTHER than MAME that are much faster. RAINE is a good example. 200-400MHz x86-32 CISC is more than enough to emulate most games with RAINE. 200MHz ARM with some slight frameskip should work a treat on GP2X.