Could anyone tell me if you can run XT Shimano rear mech with xt front and sram cassette and chain? Or would you stick with Xt through, its just that someone has recommended getting a Sram 990 rear cassette and chain, but I have just forked out on the Xt stuff a few months ago

i think you'll have no trouble running it!!!the powerlink in the chain,is a godsend(no more fiddling with the shimano pins)+you can take the chain off to clean it!!!i have an sram chain onto shimano cassette,with truvativ stylo chainset.no problems!!!

sram stuff will be fine – as is your XT stuff (or is it worn out ?)

do get a powerlink though, they ARE great (& fit shimano chains fine IME)