I've actually gone wide to mid-wide.
When I first went shopping (not knowing any better) two shops both recommended wide boards with my size 11s. I ended up with a 158 Ride Fleetwood which sits at 265 cm waist width.
Due to some unfortunate circumstances, I was forced to by another board. I read posts on here and elsewhere and a mid-wide in the 250-260 waist width range for normal, non-hard carving riders was a recommended setup. So I ran across a great end of season deal on an Arbor Element 161 which measures 254. Even though the 161 was longer, the weight loss (either due to board composition or the elimination of the board material made the board feel much snappier and controllable, as a result quicker, easier turns. If that makes any sense. How I felt on it however, might be different than how you would feel. I just know that the Arbor feels damn light though.
I run 24/-6 on my angles with 32 Prion size 11s and with boots buckled in it looks like the toe and heel angles hit like 80 degrees. I know I'll probably never ride that steep of a carve.
Also, someone else could confirm this, but I don't see how waist width would matter much if its a park board. Meaning that I only think it plays a huge role in the powder/carving/freeride arena.