Whichever one I get, the 4850 or 4870, I still don't know which brand/model to get? Is XFX the undisputed king and if so does it have more to do with their warranty than card performance? Newegg has quite a few video card combos, but I don't know enough about the other companies - Sapphire, HIS, etc.
I went with the 4870 choose asus because it came with with aftermarket cooling idles at 43c under load temps go up to around 65c. Also I have dealt with asus customer service and fortunately the few encounters that I have had to deal with them where smooth they replaced the products I have had go bad without any incident. Although I did have to pay for 1 way shipping
but I also had to upgrade my power supply I had a 500 watt ultra ps that couldn't handle the load and would randomly reboot the pc during games. Before you make a choice check to make sure your current power supply can handle the load and find out if it can supply enough power on the 12v rails my new power supply is corsair 750tx it puts out over 60 amperes on the 12v rail more than enough for 1 video card
I would reccomend the 4870 over the 4850 as the price difference is marginal. Get a card with a decent warranty, becuase in essence probably don't make that much of difference, however I would reccomend go with a reasonably popular brand.