Suspicion set up actually plays a big part, particular the front. Most of the better twin suspension push bikes have a front suspension lock out for this reason.
Ive ridden a lot of pretty fast motorbikes over the years including a turbo Gsx1300r hayabusa. They all seem to get to 200-220isk very fast but after that the resistance is pretty strong. 270 onwards is a slow climb, at least for road going motorcycles.
Such a tiny bike the Indian is that he used to fold into as well. Amazing man. John Britten basically built every part of his bike and beat the might of the major brands. At his first run at Daytona the rider was toying with the other bikes, he could, and was passing them at will...even on the back wheel..lol. There is a video on his and the bikes story available from somewhere, maybe Duke??
It must be something in the water over there.