Well the review of the Asus MyPal 620 is at....
The free GBA emulator can be found on this link http://www.pocketgamer.org/games/emulators/index.shtml but the GBA module on Morphgear is very good but costs money to buy the working module.
Not all GBA games run full speed. Thankfully for me Mario Kart Advanced does with sound, Mario Land Advance is a fraction too slow but i play the SNES version which is 100% the same anyway. I completed Wariowear recently BUT the latest GBA games sound doesnt seem to work properly on the GBA emulators because of different channels or something like that.
I play a fair few GBA games, just completed Baldurs Gate: Dark Alliance which was superb but again without sound on the PPC.
The Asus is fast enough to play most GBA games but again the later games have sound issues. You'll also be impressed by all the other emulators. If you have the money Morphgear is a fine program with a ton of different emulators.
The Dell x3 i think it is is cheaper than the Asus but the Asus still is faster and you dont need to overclock it. Let me know how you get on