Well as far as the GBA stuff goes all the 8bit emulators run full speed unless something is wrong, and you're right that the 16bit stuff (SNES and TG16) are slow somewhat.

On the DS though a fair few have tried to port over the GBA emulators, or use their core and rewrite for the DS format while others have done new things.

NESDS, SNESDS, and a few others are ports of the loopy/flubba PocketNES/SNES Advance platforms. On top of that there is now a fully supported SCUMM emulator so you can run Indiana Jones, Monkey Island, etc on there. You may just want to try and slide around ds.qj.net a bit and see what pops up in the archives as there's been considerable work so far, just not as far as the GBA as the DS as far as getting devkits that are easy to use and not a pain isn't so far along as the GBA.