One's definition of "playable speed" may be different from the next. Currently, I'd say 100% on something like frameskip 4 or 5, which is jumpy at best. It may be playable until you get the airship, which will probably skip around the world (since the emulator has a problem with Mode7). I wouldn't buy something just because something might be developed for it. I just don't want you to make the purchase and regret it.
But if you're a Final Fantasy fan, you're in luck - Final Fantasy 3j for the NES at full speed with sound (precessor to FF5), and the remakes of FF1 and FF2j, what you receive with Final Fantasy Origins, are yours at full speed without sound on the Wonderswan Colour emulator. All of them have translations (except FF1 which is partial, but the same story).
Additionally for Squaresoft fans, we have Final Fantasy Adventure (Final Fantasy Gaiden: Seiken Densetsu) and the Final Fantasy Legend trilogy (Saga 1-3) available at full speed with sound on the Gameboy / Gameboy Colour emulator.
There's also a load of other RPGs available. Be sure to check out the DW1&2 and DW3 remakes on GBC, as well as DW4 on NES.
As much as SNES9xGP may tilt the scale for many a potentional GP32 user, don't make it the crux of your decision.