Radeon 6850 or 6570 or ? for HD video editing?

APPROXIMATE PURCHASE DATE: this week BUDGET RANGE: Less than $250
USAGE FROM MOST TO LEAST IMPORTANT:
1. HD Video editing
2. Windows Media Center recording and viewing
3. Multitasking database, file management,Internet browsing and the like.
GPU, POWER SUPPLY, etc: Vendor is recommending an Asus P8P67 DLX-3 motherboard with an Intel i7 2600K CPU and a CoolMax 700W PSU. 8GB DDR3 1600 MHz memory

If anybody wants to comment on those components, please have at it. My main concern, however, is to obtain the best machine under $2000 for HD video transcoding and editing. To the extend the GPU is relevant for performing these tasks, is the 6850 markedly better than the 6570? Are there other Radeon cards which would be preferable?

OVERCLOCKING: No
Not interested in Multiple cards.

MONITOR RESOLUTION: 1920x1200 (although I occasionally tease myself with thoughts of a 2560x1440 Ultrasharp)

I'll be running 2 monitors, using DVI and HDMI.

When I buy my own parts, I use Newegg, but the vendor has his own suppliers.

Someone can comment on the video card selection as to whether or not Amd or Nvidia is better for video editing idk.
What i will say is do not buy a Coolmax psu = crap!
Antec,Corsair,XFX,OZC,and Seasonic are much better.
I would also recommend 16GB of ram if your #1 use is video editing.

+ 6790