Is it possible/advisable to run a new 9 speed XT crankset with an 8 speed chain (Sram PC-68) and cassette (XT)?

I run 9 speed cassette and chain and 8 speed chainset with no problems at all..... it is sort of the same thing.
try it and see.

The problem with my way round is that I will be running a wide chain on a narrow system which, in theory, could mean chainsuck problems.

I could source some 8 speed XT but I want to move away from square tapers...

No, you really will be fine*. Lots of people on this forum are running '9 speed' chainrings with 8 speed everything else. Including me.

I'm not actually convinced that 9 speed chainring teeth are any thinner than 8 speed. I accept that they could be, but I'm not sure they really are in practice.

* this does not form a warranty though...

Chears for the help. Just need to decided on LX or XT now.

LX.

Sorry, disregard that. You should also consider Deore tapered.

Things to bear in mind:

LX and Deore weigh about the same. XT is a little lighter.

I think XT comes with all alloy rings, and Deore with all steel. LX I have heard of severe wear problems on the middle ring. Steel could last longer than alloy.

However, I don't run any of these as I'm still in square taper world running the Alivio my bike came with. So you'll need to do some more research...

Good luck.

chain suxk would come with running an 8speed chainset with 9speed chain, cassette etc, as the chain is narrower and would detach from the teeth less easily! i run XTR 9speed with 8 speed XTR casette and a pc91 8speed chain, get the occasional chainsuck, but this is more a dodgy front mech problem i think!!! still i'd avoid 9 speed at all costs, fine unless you every go near any thing with the lable 'mud' on it!!