There are fairness and skin drag you can deal with. When I was racing Olympic class FD sailboats there were guys fairing the hulls with a Ibeam and dial indicator's to .001". Lots of work but in a 2 mile down wind leg it was a 1 to 2 boat lenght gain aginst a stock hull. Most were faired by eye and the true difference was less.
The skin is much harder to gain because the transtion from lamineer to trubulant flow changes with speed that is were you put the rough skin treatment. I would say deal with the front 1/3 of the kayak lots and 600 wet and dry the bottom and practice,practice,practice.
Don