As a point of concideration with regard to D10 E9/C6 vs S12U E9/B6 in practical use, as I listen to steel radio and many pro/semi-pro steel player CD's I've picked up over the years, I'm not hearing anything done on D10 that can't be done on S12U, and vice-versa.
So I think it is really more a point of personal preference than anything else... which is a good thing!
Good point, Pete. I've come across stuff that I really wish I had a D string for, but it's almost always when I'm trying to play something non-traditional.
Yeah Ed, that's kind of what I've been waiting for.
They probably just tune all the thirds of all the changes flat and don't play them that way when they're not thirds just like they do on Double Neck 10s.