Mike, a couple of ideas. My personal opinion is that part of the problem with faster twist barrels like the 1-20 is due to the sabot not being able to grip the bullet hard enough to keep it from slipping. A tighter combination and perhaps knurling the bullets might help. There also is a mistake idea floating around that you can not over stabilize a bullet, it is true that they will go much farther in that direction than they will when under stabilized but they can be over stabilized and also the faster you spin them the more critical a perfect bullet that is perfectly centered becomes and getting a bullet perfectly centered is unlikely when putting it in a sabot.
If some one could come up with a gain twist barrel in a 45 caliber it might be interesting to see if it relieved some of these problems.