Actually, Buell raced a 1125R on the 2009 AMA Daytona SportBike Championship against 600cc Inline4 bikes, like the R6, GSXR600 etc.
It made about the same amount of hp, more torque etc. People like European magazine test riders (neutral) that rode both, said that the Buell had an X amount of advantages over the I4s, but also X amount of disadvantages, thus making it a fair to race side by side in their opinion.
Buell also released a race-specific 1125RR version (notice the second R) in 2009, to compete in the AMA Superbike series, against the likes of GSXR1000, R1 etc.