The 6R revs up quicker, but the old "no replacement for displacement" catches up. I actually pull a couple bike lengths against the Gixxer when we roll on, but because the 6R revs up quicker I'm shifting when the Gixxer is just winding out so he ends up passing me through the gears. The Gixxer just has more peak power and you can't overcome that in a straight line, although I come a lot closer than any of my R6 or pre-2003 6R buddies do against him. As for handling, the 6R feels like a scalpel... it goes left-right transitions WAY quicker than the Gixxer. It's just much sharper and seems smaller, more like a 250 2-stroke.
The 6R is sharper and more focussed, the 750 just plain has more nuts in a straight line. Side by side, hard to argue - the 6R looks better. It's the trickest-looking bike around imo. Gixxer looks good, 6R looks newer, fresher, more hardcore. Both great bikes, what can I say.
"Keep yer feet on the pegs and your right hand cranked."