I'm looking to buy a SRAM X.9 rear mech for my S-Works (17" frame) but should I get a long cage or a medium cage mech? And what's the difference anyway?

Kato, Pad has a question for you:-)

I'll have a guess as Kato's not here. They're probably the same as Shimano ones so you'll want a long cage unless you're running a double chainset or a close ratio cassette.

The long cage just takes up the slack chain when you're in say 22/17 and gives out a bit more chain when yo're in 44/20. If you don't ride in the extremes then you can use a medium cage mech, which would mean that you 'lose' a few gears, but they're probably ones you won't use anyway.

Be aware that Shimano mechs don't like 34t cassettes on Spesh's, I don't know if that's also the case with SRAM.

"Be aware that Shimano mechs don't like 34t cassettes on Spesh's"

???

Mine works fine...

Mine works ok as well, although I'm not a big fan of 34's anyway.

Cheers chaps, looks like it's going to be the long cage model then!