I typically don't see a reason with modern rims to go 36h unless you're extremely heavy or touring, at 275lb I've broken 1 spoke on my mtb in 3 years of hard riding and those came 15g which I wouldn't build with for someone my size. Well built modern wheels just don't seem to need that many. But, since you already have the hub, if it's a good one, I would go the 36; unless I wanted an excuse to get a DT, White industries, i9, etc. It won't be significantly heavier, about 12g, and still strong.