RE: Footstrap width
I think it depends a lot on how you wear your straps. Most pro level wave sailors tend to runt them VERY big but prefer them super tight on the sides on their custom boards. This allows you to have a fairly snug fit but to still be able to move your feet in an out. Compared to this, 6" is actually on the wide side, I would say. But being a fellow cold water sailor, I can see you problem (though I never had problems with a production board).
Before moving straps, I would look into what kind of booties you wear. Many are just too sturdy and wide with a lot of grippy rubber on the side of the feet. I would say THIS is the real problem in most cases. Before I found the ATAN brand booties which I now use and which just kills everything else I tried for smoothness and comfort, I used to grind away rubber materaial from the sides of my booties with a power belt grinder and then sprayed some silicone on them in this area to make them less grippy. That worked out OK, but nothing like the ATAN stuff. The Atan boots come in 4mm and 7mm and are made out of real natural latex. Just a thin layer of grippy material around the neoprene sock. You can even turn them inside out to dry them.