I have an Ultegra GS derailleur on an 11-30 cassette. It grumbles a little on the 30- tooth cog even with the b-screw most of the way in, but it shifts just fine. By grumbling I mean that the guide pulley is close enough to the cog that it makes a grumbling noise as the chain wraps first one way then the other, with the pulley nearly touching the teeth of the cog. I don't use the 30-tooth cog much, so it's not a big problem for me, but using a MTB derailleur would be a bit better in the 32-tooth case - they're built for extreme ranges of cassette.