The Busa basically has a GSXR frame. Peel off the bodywork and gas tank, and you see a monster Gixxer. I never owned a GSXR-1100; my old bike, which I bought new, was an ancient '82 GS1100E. It and the Busa are totally different machines.
But functionally, the difference between a GS1100E, a GSXR-1100, OR a Busa; VS a real track bike I.E. an R6, R1, GSXR-750, or 929RR, is 100+ lbs. of weight. You're talking about over-500 lb. bikes VS. under-400 lb. bikes. I love the big bikes, they are loads of fun on the highway. But if you want a real track bike, you can't hide the weight. It's simple physics.