What masts do you ride? What type of sailing you do?
4.8 and 5.2 are a bit close yeah. 5.6 the diff will be important and your board will carry it very well. If you freestyle though 5.6 can have a longer clew watch for that and moves will be slower.
105 + 5.6 and good technique will try you planing at 18 knots. Possibly 16-17 but you may not stay upwind