As the x-owner of a 7mm and 10 year owner of the STW. If you put each case on a level playing field. I'm talking target barrel, blah, blah blah everything identical.
I don't believe that one of those case designs is inherantly more accurate than the other. I will tell you that the STW can get 100-150 fps faster than the 7mag. When the 7mag is popping the primers the STW isn't stressing at all. The 7 mag doesn't have the case capacity to take advantage of the slowest powders.