Cat,
Good luck. It seems that if you paper patch for anything other than a .45 you're the only person in the world trying that caliber.
You might benefit from .38-55 shooters. That's very similar to .375 Win in case size/shape. If you're considering 4227 I'm guessing you have velocity limitations?
Otherwise I thought RL-7 was the favorite for .375 Win shooters. I don't have a .375 of either flavor, but I was very near buying one. Let a '94 Big Bore slip by for $350! But I got a .35 Whelen instead - try to find another paper-patcher for .35 Whelen.