Your peak memory is 26GB. That’s far larger than ANY GPU could possibly render. When rendering with GPU you are limited to the available vRAM of the smallest card.
For your information, I get faster, less noisy images with 2.70 then with 2.73.
Also, have you tried rendering different layers at a time? Maybe some objects that don’t reflect/get reflected could be moved to a different layer and could be rendered with your CPU simultaneously (with multiple blender’s open at a time) or rendered at a different time. I read it somewhere, can’t find where though.