Easy answer for this one, 7850 2gb. As you only game in 1650x1050 at the moment this card will run everything on max quite easy with a slight overclock. And when you get you 1080p monitor, just put another in if you don't think its up to the job, by that point they will be even cheaper anyway.
more than 680 performance for like what could cost £250
more than 680 performance for like what could cost £250