Quote Originally Posted by redrhodie View Post
I just got the 11-28T 6700 cassette a couple of weeks ago, and I'm using it with an Ultegra long cage derailleur from 2007 (not sure if it's 6600, though--can't find a model # on it, but it's definitely not a 6700). It works just fine. I've done a few hilly rides, and haven't had to have it adjusted yet.
Well...this is good news to hear! And I just realized that in my last post, I stated that I could just buy an 11-28t 6600 cassette - ummm, no such animal exists, so my apologies for incorrectly stating that. Looks like I will have to investigate this matter a bit further.

I'm fairly certain that I need a different RD in order to get this to work...because based on what I've been told by 2 different LBS's, my stock Ultegra SL 6600 rear derailleur does not have enough range to accommodate a 28 tooth (or even a 27 tooth) cog...I was told that I am "maxed out" on my RD with my current 12-25 cassette. And since I definitely need a new cassette (mine is worn - new chain is skipping)...I need to figure out what to do ASAP.