As always, engine choice depends on what you plan to do with it. At under 6 lbs all up, it will fly fine with a nice 46, but as you said, it won't have enough power for 3D.

Note: we didn't need more than 3/8-1/2 throttle stick most of the time with the YS63. Except for vertical stuff and 3D. It's just a more impressive overall plane, IMHO, with the added power, as it becomes more versatile.