I have cut Graf's and Winchester brass in half and the thickness along the length varies some. Probably no difference in ballistics though. The weight variation of a batch of brass would be more important as this will directly affect the volume of the case and pressure. Thinking theoretically the best brass would have the least tolerance in weight.

I have never heard of anyone here trimming 30/40 brass. If it never is an issue it may because Krags do not operate at the higher pressures of other rifles.
I am thinking that having all your brass segregated as to weight and or manufacturer is more important than who made it.