I run a similar pace to doozerdave, but I'm usually riding with him.
16 - 16.5km/h will leave more people winded and tired than it will leave still feeling refreshed. There are folks that can ride the hydrocut a helluva lot faster than that and not be too tired afterwards.
It really depends on your personal fitness level, skill level and familiarity with the trails. It helps to know where you can afford to push harder because you have a nice "rolling break" section coming up to use as recovery.
I suppose you could say that a "fast average speed" would be in the range of 17.5km/h, You'd still get passed by some riders but you'd be doing the majority of the passing. (this assumes you are going to ride the whole system without stops) Be sure not to omit Adams Run from the itinerary, it's often tempting to skip it by the time you just finished climbing kreepy and bootleg!
If you are planning on blasting all the singletrack with a break after each blast, you could no doubt push that quite a bit.
Cheers,