I think you made the right choise! That $350 will buy you another sail which is much more important when moving from a longboard to a shortboard.
It is very important to acknowledge not only the the wind strength and weight, but also the skill level. For a shortboard novice a few additional liters are helpful, and the technora construction is easier to repair when it inevitably gets dinged. If there is any performance difference between the two constructions you are unlikely to notice it in the short term :-)