Personally would choose the Radeon 3850HD mainly because my friend has that card and it produces very nice stuff!
i have 8600GTS 512Mb and it works well for me. I dont know about your second choise because iam not familiar with it but all i can say that 8600gts is ok card. However, i would recommend saving money up and going for 8800GT or new gts. You wouldnt regret wating.
The HD3850 is pretty much the same bang for buck as an 8800GT, so I don't really see any issues with buying that. Xlink, if you ever do go sub-zero, read up well. There are a number of small things that can trip you up. And in this case, worst case scenario can be a bad one.
