Is there anything other than the obvious: length, weight/swing weight and stiffness that effects performance? At present- my main focus/aim is to find the shortest, lightest board I can that still paddles into waves well.
One of the most important thing is the construction. The connexion between the board and the foil has to be strong and responsive. Same with the deck, if it is too soft, the transfer won't be as efficient. This is why carbone board are so polular.
I don't think the shorter, the better. I've been playing with different lenght : 4'0, 4'3, 4'6, 4'10
I like 4'3 and 4'6, not only for paddling, I like it for turning, it gives me more drive and more shortboard feeling (maybe just seing the nose of the board in front of me reminds me surfing).
I like to keep the same volume as my shortboard (a bit less actually but I don't want to go too extrem).
Double concave, beveled/concave rail, etc... I don't know if it makes a huge difference, it is definetly super rad and fancy, it reminds me of a cool space ship !
I think it does make a difference when touching down and hitting the white, it doesn't stick at tall. With my old board no double concave I was fine. But I guess at the end, all those those details make the difference into your performance.
What I like and I won't go back, is the little recess deck, super comfortable paddling (locked in) and less foam undr your feet.