I thought the 9 and 12 both had the same top speed. I know the 12 is geared taller, but I thought it was to make up for the lower redline.
The weight isn't too different. I think it's 10lbs, and half of that is in the exhaust because the 12 has a valve and is double sleeved. If you switch to an aftermarket exhaust they'd be pretty much the same. Haven't gotten to ride an xb12 yet, but coming from a 600, I think I'd definitely like to trade my xb9 in for one someday. I love my bike, but definitely pictured something a little stronger when I bought it. I drove 5 hours both ways to pick it up, so I didn't get a test ride. If I had I probably would've considered holding out for a 12.