Can someone give an opinion on the 450 GPU's - they are not on the list and I am seeing them on sale for around $100. I am looking replace a 8600gts in an old HP that I have upgraded the PSU with a corsair 550 watt., Have tried ATI GPU's, but for "what ever reason" the MOBO, RAM, or what ever doesn't like them - so will now try an Nvidia GPU.