I have both barrels also, but I didn't have time to work up a load in my 7-30 barrel.
I did have a few boxes of 375 Win factory loads though, and the 200 grain loads give me a 1.5" group at 100 yards in my 12" barrel with a 2-6 Bushnell scope. Minute of deer to me, so I was set.
I took the Contender last Saturday morning, opening day in VA., and about 8:30 a nice little small buck walks straight on to me. At about 40 yards I shot it just off center of the chest. Found the bullet against the hide in the lower part of the hind leg. It had taken out part of the right sholder, a 1/2 dozen or more ribs, and 1 lung and part of the heart on the way. It weighed about 185 grains, and expanded to .600 before it quit.
I am pleased as can be with the factory 375 load, and since they are hard to find now, I plan on loading my own for it and the 7-30 before next year.
I have some wheelwieght, and some harder casting material and the Lee mold for the 375 that I want to tinker with also.
If you take either barrel, I think you'll do fine, but if you have the 375 sighted in, and since you have already tried the 7-30, the 375 gets my vote.
I also just wanted to post how pleased I was with the 375 Winchester.
Good luck Saturday. Andy