Are you certain the Mustang needs medium scale? The one I had (albeit many years ago) was a 30" scale and used short scale strings.
I've used the Rotos on my SX shorties - I like the feel, but that's not saying you will. They're soft to the touch without being floppy, if that makes sense. Silk on the ends is a very pretty medium blue. Again, that's for short scale. Not sure about the medium scale versions.
Blooz
