You also need to factor in how much faster you will be on descents with a suspension fork, as well as the conserved energy form not getting the crap beat out of you everyday across 5 days.
I think it is pretty well-established doctrine that a suspension fork lets you be faster / safer / more comfortable vs. a rigid fork.
As Chad noted, focus on fast tires and other opportunities to improve aerodynamics (including potentially an aero road lid).