I would imagine that you would have so/so results with RG6, but it is designed as a pre-amplified signal carrier. The gauge of the center (core) conductor is pretty darn thin - not sure - what is it, about 22 gauge? It just isn't thick enough to carry the power necessary to the speakers in a decent setup, and the cost isn't a savings over cheap 16 gauge speaker wire for sure, which will provide much better power flow.
RG-6 is excellent for carrying video and audio signals before amplification, but I hope I am not the only one who will suggest that it never be used as actual speaker wire coming out of your amp.
Heck, I'm not even sure how you would cleanly terminate it at the amplifier and the speaker. Pretty tough to get RG-6 into a binding post I would think. A lot of insulation for a teeny-tiny wire in the middle.