I just happened to catch this thread. When I talk Aprilias its on the best Aprilia forum in the land
here.
IMO these are both VERY FINE bikes. Of course the Japs always copy, and the RC51 is more of a Ducati clone(90deg motor) than an Aprilia clone. I hear a lot of hard to setup talk on the RC, but the Aprilia can be finicky if you go the wrong way.
The motors torque and hp I believe are similar, although each have their own identity.
Styling wise, IMO, the Italian Stallion Aprilia wins hands down.
Its a drop dead gorgeous bike.
Definitely a hard choice!
But
I own an Aprilia...
