I think the XL in the Patagonia Capilen 1 Bottoms should be a good fit for you. I'm in a large at 6'1" and I think even the large would fit a taller dude, so at 6'5 you should be good to go in an XL. Great lightweight bottom, you'll be stoked.

i'm 6'4", 36" inseam, and they work fine for me. just don't expect them to keep your junk in without a supporting cast...