i recently did some hand quilting with perle cotton.
if you are a handquilter, you are probably going to find it difficult to adjust your stitch length. my perle cotton stitches ended up being pretty close to my hand quilting stitch length. the body just remembers.
i also had a hell of a time with needles. perle cotton is thicker, but you need a nice sharp needle. the combination of a larger eye and a sharp point meant a longer needle, which was pretty hard to get used to. it didn;t go a whole lot faster, but the stitching is certainly more visible.
needling the newer wool bats is a dream. i love it.
not sure i would use upholstery thread. i think i'd be worried about it tearing my cottons. maybe. not sure. test it out and see how it lies
aileen