To answer my own questions (for the rest of you)
1. Is the GBA Expansion memory volatile or NOR like the 3 in 1?
Volatile, games load very fast and are not kept in memory after reboot.
2. I have read that GBA support is buggy, but cannot find anything concrete except some complaints about real-time-save (which I dont care about). Is this the only GBA issue?
GBA games, the ones I have tested so far, seem to run flawlessly.
3. I understand that the GBA Expansion saves to a battery, and backs that save up on reboot. Is there a way to force that save to backup without rebooting? (I.E. a 'Save' button combination)
There doesnt seem to be a method to do this.
4. Does the GBA Expansion use raw '.sav' files that are compatible with VGBA or Supercard? (I.E. can I use my Supercard SD GBA saves on the M3DS-R GBA Expansion without conversion?)
Simply renaming VBA or Supercard SD saves, both GBA and NDS, to use a .0 file extension, and they work perfectly, no conversion needed.
5. Is GBA support fullspeed? My Supercard SD runs many games (Final Fantasy VI, FFTA, Megaman Zero, etc...) much slower then the actual cart would run them.
The Final Fantasy games I have tested, that were slow on the Supercard SD, seem to be full speed on the M3 Real.