No, don't get that card, I don't recommend it. I recommend you 6770/5770 1GB only, because that'd save money much (preferably for your upgrade of your CPU). Your card is maybe $150, while 6770/5770 1GB is maybe just below $120. Therefore it has the same performance. 2GB is also useless at your resolution really.
6770/5770 needs something like this:http://www.newegg.com/Product/Product.aspx?Item=N82E16817371033
Seems OK with your configuration (5770/6770), it should play Crysis 2 & Anno 2070, but not 90 fps maxed, we don't really need 90, 40 is even enough.
Oh yes, make sure you have the non slim version of the dell.
Whatever you do, just good luck
Here is a good 6770:http://www.newegg.com/Product/Product.aspx?Item=N82E16814121474