I think you may be OK.  However I would advise that you put in the GPUs one at a time and reboot the computer and make sure the card gets recognized/mines correctly etc.  If you put all 5 in and something doesn't work right, you will have a hell of a time diagnosing the problem.  I would also recommend that once you have the machine dialed in and it works reliably, to lower the voltage of the cards to prolong the life of the PSUs.

Just wanted to add my full support for Middlecoin.  Been mining since the last week of December and have nothing but glowing things to say about this pool.  Even though it can get a bit antsy on this forum when stats go offline or unexchanged builds too high, I don't lose faith because I get paid in BTC at the end of the day.  LOVE it, keep it up H2O!

Gorgeous car, wish I had the coin!