You have to ask yourself what you expect to get from carbon stays, or what you expect to lose by not having them.
My feeling is that you are hoping to save some weight by using carbon stays. This can't possibly save more than perhaps half a pound. In the big picture of your body weight, this amounts to exactly nothing. And along with that gain of nothing, you also get more flex, less reliability, shorter lifespan, and the exciting prospect of sudden catastrophic failure. Carbon has its place, but the chainstays of an off-road bike to be used by a really big guy don't seem like that place to me.