Broke the mains in my gut/poly hybrid earlier today. It was 16g Prince gut mains with 17g 4G crosses. The setup lasted roughly 6 hours of play.
Besides the lack of durability, the setup played amazing. Not overpowered like I thought it would be. Very spinny initially but after the 2nd hour the mains weren't snapping back as well. I think a thicker and slicker cross might be the ticket as Drakulie had mentioned. I think I'll try RPM 16g next as a cross. Not worried about tension loss because I think the gut will break before any drastic change in tension. If I can get 8-10 hours outta the gut/RPM, I'll be happy.