Originally Posted by wingnutt
A few things - first of all, Ultegra and D/A can handle up to a 30 tooth cog. I have 13 / 30 with my Ultegra 9 speed and it works like an absolute champ. I'd recommend this gear if you want to do some serious climbing over the 27. The 27 is only 7.4% lower than a 25, so it's not a huge difference.
YES!!! I have Ultegra 8-speed on one of my bikes. For the big mountains, I use a stock 11-30 MTB cassette.
I also have Dura-Ace 6-speed on another and use a custom 13-30 freewheel when I hit the mountains.