1978 85 hp johnson javelin on a 17' dixie. 900 lb hull weight.  i am getting 5150 - 5200 rpm and 39.2 mph (gps) at WOT.  Added a 260 lb friend and 2' waves, and was getting 4900 and 36 ish.  I'm moving to wv in a few weeks, and I figure the added elevation, and cooler water/air temps will bump up my rpm. Would you guys recommend dropping to a 13.25 x 15p prop, or just keep the 13.25 x 17p?

If that's all the rpm you're turning, I would drop to a 15 even if I wasn't moving.  You are already on prop size too large.