Be proud of your choice. Yeah in Benchmark nForce2 do beat KT400 in every aspect (including price), but you already purchased one, so be content to it. To me buying a A7N8x to replace A7V8X is total stupid, even your existing mobo is free you should save the money. Cash is hard to be earned.
Or may be you just want to know which one is better, then the answer is A7N8X.
You never know how stupid you are until you have done something stupid enough for you to realize it.
<A HREF="http://www.anandtech.com/mysystemrig.html?id=22996" target="_new">My System Rig</A>