I've heard that the 7xxx series is coming out this year so when it does come out any idea how much of a drop in price the 6xxx series will get?
Well it's tough to say. I'll give you an example.
When the 5850s first came out, they were limited in stock due to the fab process or something of that nature. They were pretty cheap at the start (around $280 or so) but when I got around to buying one, I had to end up shelling $360 instead because of demand>supply. Having that said, it's hard to gauge what sort of price drop we can expect if demand is still driving high, especially if the 7xxx is bad at mining (and things are pointing that to be the case).
I think you can expect 20-50 drop in price that may or may not shoot back up as per the demand. It's all speculation at this point.