I would go with 6hp..I have a Columbia 22 displacement 2200lbs. I use a 4hp Yamaha and wished at times I had 6hp...The 4hp can be a bit slow getting to
"Rudder Speed" some marina's are tight and its best to get enough speed fast to get rudder...Also going out or coming in against a tide can be a bit of a grind..Not another feeling in the world like having almost full throttle and no head way......You will also tire of an inboard tank should you get a few miles out and boom the wind drops to zero, the extra fuel is worth it,trust me