I'm 6'2" and ride a 610S size Sherpa on which I am very comfortable, couple of photos and some info on
this thread.
In an ideal world I would maybe have liked an inch or so more length on the seat tube and the head tube, but purely from an aesthetic point of view to reduce the amount of visible seatpost and steerer spacers, but that is the largest Sherpa frame available so I'm happy with it.
At 6' you would probably be ok with the 535L size as long as you are happy with a similar amount of visible seatpost and maybe more steerer spacers. The 'virtual' top tube length at 575mm is the same as mine, and I like it (I use drop bars), some may prefer a longer reach.
Basically, if the price is hard to beat, I think you will be fine with that frame size, and if it turns out you feel it's not right you could sell the frame on and get a larger one or maybe a Surly LHT frame which are available a bit cheaper than the Sherpa frames but pretty much equivalent, if not higher in spec.