Depending on the price difference between Z68 and P67, I would prefer the Z68 just for the fact that it can run without a dedicated video card (if you experience problems with it for example or if you want to retire your machine as a server/htpc). Just something to keep in mind.
Thnz for your in formation. Yes, you are right. I should buy Z68 even though I can't get better performance from that.
It will be useful in other ways.