I have a 2012 Specialized rockhopper comp 29er,and after bending the Octalink bb I want to upgrade my crankset to XTR with the larger bb shaft,yet I have a shimano Acera front derailer and chainset and shifters and a Deore shadow rear derailer.

Now as long as I get a XTR chain set for 9 speed then can I drop this crank set in?

Also why are there so many XT rear and front derailers as cheap as $10 if XT is the top range under XTR??

And how does this compatability thing work between different components?