Nothing is overkill. Ever. I personally overclock my parts to the limit of my budget (best coolers I can afford and any temps under 100C) and I still find that a single 7970 isn't enough for my 1440p monitor. I often lower settigns in game purely because crossing below the threshold of my monitor's refresh rate is extremely noticeable for me and it bothers me more than it should. I have been putting money aside for a second 7970 at the end of the month and a custom water cooling loop by the end of March. The general rule is that you should always buy the most powerful graphics card(s) that you can afford or you WILL regret it later.