Couldn't get the right settings in the drop downs, so I didn't add my results.
I've just put together a Sandybridge 2600 3.4Ghz (although the bios says its running at 3.8?? and Win7 Pro 64bit is saying 3.7. I haven't done anything to the bios, so maybe it was upped at the warehouse I bought it from). 8gig of Ram (should be 16, but had a miss matched set of pairs so returned).
Completely clean install, only TG, I got 7:41.
When I decreased the bucket size to 64 (although it looked like it was rendering 128) I got 7:12.
To upgrade form my previous system which had a decent graphics card that I carried over, the cost was £700.