What adverse effect would having a custom drilled wheel pattern have on the integrity of a wheel?

Reason I ask is there is a deal on Rota Slipstreams on the groupbuycenter. $450 shipped for 15s and $600 for 16s but you need 10 people to order a custom wheel pattern (the Focus has a funky 4X108 pattern). I was thinking these would make a nice autocross wheel.