[Jack]

Another hitch in the 'use a single bullet weight' theory is that not all 140 grain bullets may shoot to the same point- in fact, I'd be quite surprised if they do.
So, you'll hafta re zero when you change bullets, even if they're both 140's. And, as Brit hunter pointed out, the trajectory of different bullets may not be the same, either.
So, since you gotta re zero, anyway, you don't lose anything by changing bullet weights at the same time.
I do like the idea of matching the bullet to the game. In my 280, I use 140 Nosler Ballistic Tips for deer. If I ever got a chance at elk or moose, I'd switch to a 160 Fail Safe, which I don't think is made in 140 grain weight.