I actually oc'ed it to about 3.8ghz but went with just normal speed because I just thought I do get decent frames with just the normal speeds. Will i experience bottleneck if I won't overclock it?
You'll have to see exactly where, but if you already know how to OC it, then if you do notice some slowdown in intensive games, just OC a bit. I'm guessing you won't see much difference over 3.0 or 3.2 ghz in current games when Crossfired, and look at all the headroom you have. Plus X58 has plenty of PCIe lanes. I'd definitely say that changing your mobo and cpu (and probably OS too) right now won't really give you much performance boost particularly in games. More GPU-muscle will definitely make a difference although crossfire has its issues. As far as AutoCAD goes, the OC should make a noticeable difference.