Three questions: 1. Why the hell are 4870/4890s so murderously difficult to get all of a sudden? 2. Shoul I trust ebay for this, at all, ever? 3. I can't make head nor tail of this comparison chart; can I Crossfire a 4870 with a 4770 or a 5870? Basically I'd like a second GPU but the 48xx line are proving very difficult to get a hold of.
i think the 4870 is only compatible with a 4770 on an AMD chipset (not sure on this but thats what it looks like). bear in mind that the 2 cards will match (ie a higher clocked card will downclock itself when paired with a slower card). Also the RAM will match (so a 1gb card like you have will only use half if you pair it with a 512mb card). i found this: http://www.lambda-tek.com/componentshop/index.pl?origin=gbase26.3&prodID=1736840 its powercolor but has a custom cooler and is 1gb. bit pricey though.
i dont think you can use a 5 series card, i know for sure you can pair a 4870 with a 4850 but this will pretty much run as 4850 crossfire, your best bet is to find another 4870 or what i did was to sell the 4870 and buy a pair of 5770's
