hd 6870 is much better hd 6850? for playing battlefield bad company 2 ?
How much is much?
The 6870 is better, but not a lot better.
If you had a 6850, you would not bother to change it out for a 6870.
If you have the budget, get the best card you feel comfortable buying.
a 6950 is better than either, and a 6970 is better yet...... You get the idea.