The biggest Buell is based on the 1200 XL motor.
They originally started with the XR1000 based RR1000 model.
Presently, they're all 1200, except for the 500cc Buell Blast single, but the Buell community is waiting release of the XB9R Firebolt, revealed to the public last summer. This model is all new, based on a new "twin Blast" engine. Displacement is 984cc.
More at www.Buell.com
I've been a Buell owner for 10 years. It's been fun.