Originally Posted by
Monoborracho
And I'd need a $300 SRAM XX cassette if I want to keep a mountain geared rear end.
I can't help with all your decisions, but be aware that Shimano recently announced their upcoming
10 speed XT and SLX MTB groups. You will have much lower priced cassette options than XX.
SRAM will also have 10 speed on every group from
X.7 up.