Ever heard of "professional" sniper using a semi? There must be a good reason for it but I am no expert.
I'd suggest picking up a copy of Boston's Gun Bible and reading his review of the AR-10 as well as the other three big MBRs before making your purchase. It will likely make you much more informed on the subject.
I should have mentioned Amazon has the best prices on that book. Even at MSRP it is WELL worth the cost.