They are both equally fast. the gixxer will get the busa by about a bike length in the quarter mile, but it all comes down to rider skill anyways
Here is why I picked the busa-
1) it's much more comfortable, the gixxer's are VERY cramped for me (6'4")
2) your passenger is much more comfortable on the busa, bigger seat, cushioned footpegs, butt-bar
3) the busa has a VERY distinct look. All gixxers, from the 600/750/1000 look exactly alike.
4) you get a clock and a gas guage
5) Busa hold their value MUCH better than gsxr's (if you keep it relatively stock)
6) The busa will walk that GSXR all day from about 50mph on
7) busa gets more respect, and MUCH more stares and looks from people
Mike