I say go for it. I think the "poly cutting cotton" has been labeled a myth, or at least deemed to be outdated information if it ever was true. I think it's very common for longarmers to use poly. And honestly, on all of the old quilts I've seen, it's the faces of the cotton fabric pieces that wear out well before the seams do. The fabric inside the seams is protected, after all. I don't think you need to worry about it.
Personally I
don't like the poly sheen, but I have found low-sheen poly threads that I will use in my quilts! So far the quilt police haven't arrested me.
