Yeah, if price doesn't matter then a 1080p monitor and something like an HD6950 would be a good call. If you aren't going to upgrade the monitor don't bother with anything more than the HD6850. Your PSU is fine for either.
i wouldn't get the HD 6850 or 6870 because of the microstuttering explained recently by Tomshardware, like suggested a GTX 560ti or HD 6950 will do the job at any resolution.
for the new HD 7K series, it's gonna be 28nm which means low power consumption, less heat with a 1 GHz GPU frequency and new XDR2 technology which is said to be twice faster than GDDR5, a high end model such as HD 7950 is said to be beating the HD 6990 in performance http://www.tomshardware.com/news/amd-HD-7900-XDR2-Rambu...
The 6850 and 6870 are perfectly fine cards. Microstuttering issues are only present if you Crossfire them, and there would be no point in doing so with such a low resolution. The 7000 series cards are all being pushed back to 2012 now, so unless you are okay waiting anywhere between 3 and 6 months for a graphics card, or you have a card that is still giving acceptable performance right now, you may want to consider what is available now, rather than wait.