I just wanted to point out my experience with both cards playing nothing but World of Warcraft.
My system specs:
Motherboard: MSI 890FXA-GD70
Ram: Corsair DDR 3 (4x2GB = 8GB) @ 1333mhz (due to overclock the ram mhz changed but not sure what it currently is since I am not at home)
CPU: AMD 1055T over-clocked from 2.8GHz to 3.5Ghz
CPU Cooler: Prolimatech Megahalems Rev B with Scythe Fan blowing to exhaust
Hard Drive 1 (Win7-64 ultimate and WOW): 60GB OCZ Vertex II
Hard Drive 2 (storage): Samsung T3 Spinpoint 1TB
Sound: Onboard - MSI/Realtek
PSU: Thermaltake (forgot model) 600w, modular.
My test was rather easy if not simple. I only play World of Warcraft. I am playing it with the add on string to the execute file for Directx 11 support (to be honest, not sure if it is enabled or not, I cannot really tell the difference but that is a whole other topic) I play in only 1900x1200 with all setting set to max (Ultra) and supersampling to 8x.
So I played in the same zones just at different parts of the day/night. Ran the same dungeons, with the same people. Frame rates lows for both were approx. 45fps. When I would fly around the new zones in Cataclysm, my FPS would normalize (what I normally would see with my 5770) to 60-90 fps. During Dungeons is when I started really feeling the power of both cards, my fps would burst to approx. 160 fps then drop back down to 100-120fps with the 570; however with the 6870 it would burst and hold steadily at approx. 150-180fps.
Each card got 2 days of play and the results I mentioned above remained the same if not very close to the stated fps (give or take 5fps). I did not alter the Catalyst Control Center or Nvidia Control Panel what so ever other then ensuring Vertical Sync and Triple buffering were off, otherwise they are at default settings.
I am a fan of both Nvidia and AMD/ATI however I do feel, at least in my case/situation, the 6870 performed better on my system and the cost difference was approx. $80-$100.
I will end my observation with a question for those that can give me feedback based on their experiences with WOW-Cataclysm or any other comparable game. I currently have an Asus 5770 Cucore, and I was looking to get a newer card not only for WoW, but looking into other games like Dragon Age, Rift Online (when that becomes available), FF14 (I can only run that in a very small resolution to maintain good quality graphics and high FPS), and pretty much any other big MMORPG that will come out in the near future. I was considering a second 5770 but most threads suggest that you stick to a single card solution before moving into multiple cards. My board is capable of CFX and if that would offer me better FPS at 1900x1200 with a second 5770 I do not want to rule it out. But if dishing out $100-$140 for a second 5770 really worth it? OR am I better off with a 6850/6870, 570?, maybe even 6950 if price is nice? Be mindful I am looking for best bang for buck, so lets base it off that and thanks in advanced for the help.
I'd like to point out one thing here. If you are over the hz of your monitor, you don't see any additional FPS. Your monitors refresh rate is the cap. Given your FPS, your card would run cooler and quieter with V-sync on. Enable triple buffering so if it does drop below your monitors refresh rate, you don't lose a lot more FPS.
It's weird to see the 6870 out perform the 570 in this game, as it favors Nvidia generally. The 570 will give you more performance in most games, however. But the 6870 does have some nice AA features for some games.