I think a .61 will do fine.

I started out with a .46 FX on first few flights. I did well but I felt the power was low. I took it out and am now flying it with a MVVS .77 and mini pipe set up. I like big props and this thing turns them no problem. I'm using a 14x6 and it has tons of pulling power and will accelerate going vertical. I also ran a 15x4 before and it also ran good. Just a bit close on ground clearance.

It is a little bit heavier but no different nasty habits. I used the same engine mounts and havent had any problems yet. It fits nicely in the cowl since the cowl is a pretty good size.