If you are able to formulate a hypothesis I could do a special build for, don't hesitate. Also I'm quite intrigued by the fact that you have such a large memory consumption though. Is it possible that your number includes Wine or some other layers? (and if this is the case, 32bit and 5GB won't work as you mentioned)
About the results. That's some solid numbers on a representative of the market GPU tier! So close to that sweet, sweet 60fps. I'm sure I could squeeze some more fps out of that renderer in the future.
This is tremendously valuable data for me. Once again, thank you sir!