Graham,
I've used my 7'10 Cuda with the DWP930+180speed tail. It works good for downwind sup. I think if you want to ride the 755 or smaller performance foils then a more forward box would be better. Here is a pic at the end of the run, Aiden on 7'7 with DWP755, my Cuda with the DWP930, Chris with the 6'8 and DWP755. The Cuda's are bloody good boards and the 7'8 would be a weapon for winging and sup if you are light enough to use it. I'm currently stuck on an island with just one board, one wing, one foil and one paddle. I took the Cuda with me! Quiver killer board in my opinion does it all.