well i can tell you that the GMS .47 is one hell of an engine(probably more powerful than the FX),I would go with the GMS,have had both and the GMS outperforms and outlasts the MDS by a mile.I have one installed in my Qhor,:
Specs:
32" wingspan
32"channel
ailerons ,rudder,andelevator just like you suggested(counterbalandes and about the same dimmensions)
I initially built mine with a 35" wing,but after 60 crashes or so it was pretty beat up)so I buit the second wing with the 32" wingspan,I like it better.One thing I did notice,they perform better with the CG about 3/4" behind the fold with the tank full.Hovers,harriers,flatspins,waterfalls,spins,el evators,blenders,
,IT WILL DO ANYTHING and it hovers like a dream,THE BEST 3D TRAINER,BAR NONE.,AND MOST IMPORTANTLY IT IS VIRTUALLY INDISTRUCTIBLE.Gotta love 'em
Thanks Tatoo