How the hell can you not get good speed ?
With desmume, i was able to run Pokémon Black 2 on my crappy Pentium Dual Core laptop fullspeed with OpenGL+Jit under Ubuntu.
However, the JIT and the OpenGL mode can only be enabled at command-line, like so :
desmume --cpu-mode 1 --3d-engine=2
I'm using the official build. (you can use the nighlies too)
It should work on Windows as well using a batch script or something.
If not, feel free to switch your GPD Win to Ubuntu
That being said, no$GBA is pretty fast too but its compatibility is very low.
It can on the hand emulate DSi games.