I regularly switch between Ultegra and Rival, depending on the bike. I like them both, although they each have their strengths and weaknesses, as pointed out above.

It took me a couple of test rides on a Sram-equipped bike before I felt comfortable ordering one. Go do a bunch of test rides....it's the only way to know.

On a semi-related note, have you ridden any other 6700-equipped bikes and had the same issues? Sometimes it's not the drivetrain, it's the frame.... (Not trying to talk you out of a change, just thinking out loud!)