I've been sleeping with my IX UQ for about a week and a half now. Very happy and comfortable. Like pisanodc, I'm a big guy, 6'2", 260# and a little more width would have been nice. I rigged the top and bottom with a connected rope to keep it from sliding out when sleeping diagonal and moving around. I've been comfortable in the high 40's. For me, about as cold as I would take it would be about 45 or so, but I sleep cold.
Great product, great price.