one-shot :
You can't compare a non oc'd 4870 to an o'cd GTX260 because you could just as easily overclock the 4870 and it'll beat it....for $100 cheaper. If you already have a SLI board get the Nvidia, but if you're looking for a new board get an intel chipset and Crossfire the 4870's and save money. Even with that being said, if you still bought 2 4870's you'd save $200 which would buy you a pretty nice board to give them a home.
I don't think anyone was comparing non oc-ed cards to oc-ed cards; I specifically said that the 4870s are poor overclockers at this point because of software issues. So seeing as the only way to overclock the 4870 is with either a fan mod or a new cooler entirely; that collectively quantifies basically ANYTHING other than a 4800 series as being a better overclocker than a 4800 series.
Benchmarks have already shown that the 4870 and gtx260 are nearly parallel performance in most applications, the main selling featuer of the 4870 is PRICE, and that is a damn good selling feature given that they are so close in performance. But really, graphics cards "beating" each other? Sure, if you want to make this into a fanboy thing go right ahead but I already said specifically that the 4870 is slightly more performance for less cost so it is therein the better buy unless you already have an Nforce board.
Pegasus15: They are really no more audible than the 8800 GTs which I was using before; take that as you will. I run them at 55% fan speed and I can't hear them over my antec 900s fans.
Would I recommend them for an HTPC? No, they are definitely not that quiet as the antec 900 while not extremely noisy, does have audible fans.
Pegasus15, if you are planning on operating a single video card or if you are using an Intel chipset motherboard which is crossfire compliant I would advise the 4870 over the gtx260 simply because the 4870 is cheaper for the same performance - and that is a damnably good reason to get them if you have the option.