- see what other HD6850's are selling for used. You likely can't ask more than 75% of the cost of the cheapest HD6850 that is brand new.
- Is the warranty transferrable? Probably not, however I think EVGA has warranties that apply only to the card. That would make a big difference in what you can ask for the card.
- Extras. The driver CD is useless as you'll download the latest driver from AMD anyway. As long as you advertise that nothing comes with it then who cares? Manuals are generally useless as well.
The HD7850 can use more than 1GB of VRAM in some games. In general, the more powerful the GPU the more RAM it can use. The HD6850 in theory could have used more than 1GB of VRAM but it would have been at frame rates that were too low to be enjoyable.
*In general, you want to play most games at 60FPS with VSYNC enabled (to avoid screen tearing), then tweak your settings so that it achieves VSYNC most or all of the time.
**I particularly enjoyed "Kingdoms of Amalur - Reckoning"; if you don't have it you might want to wait for it to be cheaper and include some DLC. Just FYI. The HD7850 can handle that game at 1920x1080 with everything at MAX quality.