Gorgo said..
I want to get an inflatable SUP, but basically a raceboard so I can go paddling for exercise and do the odd downwinder. I don't want to be paddling along and thinking, "This is really good for an inflatable, but I wish it wasn't one."
The Starboard and Fanatic 26" wide models are very good for what you are wanting, and I'm told the new Red 28" model is also pretty sweet.
Here is a video featuring the Starboard 12'6" x 26" Astro Racer. This is from a year ago. The current model is a little different.