Holley 4150, Need rebuild help..

Ok one more question..
Can someone school me on power valves?

I live and drive at high alt. (6,250')
my.rebuild kit has a 6.5 and a 10.5.
A 6.5 was in the carb but would I be better suited installing the 10.5 and inriching at a higher RPM, more vaccum?

Or am I simply not understanding how this valve functions?

Thanks again.