I think the throat (and the twist) on your 36 inch barrel are design designed for some really long, heavy solids. If that is true, or perhaps, regardless of the original intentions, I would use that barrel for solids.
However, just like you, I have had two different 375CT barrels at the same time one in which I was shooting 350SMK and the other 352CEB because at the time those were the best bullets you could get and I couldn’t really decide between them and I had two barrels and I felt obliged to keep using both of them. And just like you, it was a complete cluster fuck keeping track of everything and it was a mixed blessing when the N570 prematurely burned up one of those barrels. That’s when the 390 came available, and I had been wanting a bullet like that for a long time . I spent a lot of time and money figuring out that it wanted a 0.100 inch jump, but I was very happy after I did.
You may have already told us this in one of the posts above, but if I were you and you haven’t already done it, I would load up some with 132 to 134 grains of H50 BMG and set them back to a COAL = 4.290” and then let us know how they shoot.