I have built and fly both. I will say that a .61 is a ton of motor for either plane. The RV flys very well on a .46 and mine has flaps, neat extra toy. Both planes have soft landing gear and could use an aftermarket gear. I would think you would need to keep all of the weight towards the tail in either design to use the .61. Keep us posted on you build, it will be interesting to see how you fit this together, and pics would be great! Good luck.
JEB