RE: sig something extra or gp rv-4??
Go with the larger, as long as it fits.
4 stroker in a scale, always.. it's just the right thing to do!
You'll be happy with it, it is a very neat looking plane!
Look at linking the flaps togther with the usual aileron horns, to minimize teh amount of servos, and to minimize teh 'protrusion' on teh bottm of the wings..