Yes, but I onlly have 32-bit XP Pro, so I can't try 64-bit, but plan on getting Vista Ultimate in 32 and 64-bit verison package in the near future.
I tried the 1GB DDR3 4670 alone and unXFired, and it did better than the 512MB GDDR3 4670 with faster RAM MHz version. The 1GB version hit up to 43FPS or so and maybe a min. of 20 or 21FPS or so, while the 512 MB 4670 with faster MHz GDDR3 RAM version hit a max of 38 FPS or so and a min of 16FPS or so. So, I think Mussels hit the nail on the head and that is that the tighter etc. timings of the lower MHz speed RAM on the 1GB 4670 version is performing better than the faster MHz 512MB RAM of the 512MB 4670 version. Interesting. Probably the extra amount of RAM is also helping the 1GB 4670 version.
When running these two differetn 4670 versions together in XFire, when I switch to or from XFire mode in CCC the compooter has to be rebooted to calibrate the different cards with different memory sizes, so I think I will get another 1GB 4670 version and sell my two 512MB 4670 versions.