any idea why an average 6800GT PCI-E is roughly $50 more than the AGP model? same clock speeds, right? what gives? when it comes to the 6600GT or 6800ULTRA versions, prices are only $5-10 different. also, are there any issues with having two cards from different brands? say, if one is bought now and another a year and a half from now. is the SLI standard pretty set? thanks.