what have you skiied before?
I'd recommend to take whatever you want to do the most, then tailor it to it....for example park = dead center, powder = traditional
what kind of powder you talking about? if its a ton (like 20+), then get anotehr ski, but under a foot...then just adjust for this ski
so in your case mabe 3 cm back from true center, maybe put them at the recommended center just about trad