Right now I have a Limited edition 6870 1gb, but it is old and getting to the point where it is starting to struggle with the new games. A guy I know wants to sell me his used msi 6970 lighning 2gb for $150 and I could always get a new diamond 7870ghz 2gb at best buy for $260 or wait another month and get something no more that $500. would I see an increase in gaming performance between the three cards that I mentioned???