I would say low or mid with a lot of settings turned down. High will lag. I tried beta with an old gpu of mine (A GTX 260) and yeah lag with high and also with mid unless settings are turned down. This is on a resolution of 1920x1080 though.
These people had processors that are much more powerful but results should still correlate
EDIT:: in case it isn't obvious, your GPU (7700 series) is an improvement to the 6700 series. You can peg your results to that bar. Looks like you have one of the better compatible cards. (one of the few series working really well is the 7xxx-series) congrats!
ALSO:: same link as Tab54o he posted his while I was writing my first post.