"Glider pilots on the Allegheny Ridges (ridge soaring), in Western US high deserts (thermal soaring), and in the Sierra wave sometimes use higher wing loading"

Then the GP15 might be able to satisfy these US pilots as long as they use antifreeze in the ballast :-).
Also you might not be able to get all the benefits of high WL if you are limited by Vne due to high altitude.

I have been lucky to fly in Minden before.
Unless you compete in the WGC or are trying to beat a world record, 60 kg/m2 would already be A lot.

Bottom line, lets look for news from GP or the dealers to get confirmation of configuration and delivery dates...