I have some friends who are/were big bike guys. One had a gsxr750 (after he got rid of his 600ninja he learned on) and at the same time a buddy had a cbr600 f3. The guy with the gsxr ran it at an open track event in Iowa (for the first year of the SRAD on the gsxr he was invited to run it there) and he loved the bike. Another friend had a r6.
However, his thoughs on the gsxr were, the cbr is a great learner, stable, ok power, and a great resale (if you plan on stepping up in a few years). He always thought the gsxr was alittle more of a riders bike and more unstable in some area's. He thought it had alot more front end wobble issues if you were not carefull or didnt have the exp. of riding long.
He sold the gsxr a few years ago. He now has a blue R1 and he is amazed at that bike. He is convinced it would ride circles around the gsxr.
The R6 was a great bike to start on (actually 2 freinds have had r6's), however, they both noticed while riding with some of their freinds that the r6 was hard to keep up with some of the bigger bikes (of course) like the Honda rr, and R1, gsxr750's in the twisties. They felt it was all they could do just to keep up when others were riding somewhat less than all out.