120gr is getting on the heavy side for the caliber(aka lots of drag).
On the contary: "heavy-for caliber" bullets (longer=heavier if diameter remains constant) are more efficient (less drag).
I used to obsess about pushing a 130gr bullet to 3100 out of my .270 WIN.....
I found that efficient heavier bullets are going to carry more energy at 400 yards...... I read somewhere (on here, IIRC) that "Muzzle velocity is a depreciating asset, while Ballistic Coefficient and bullet weight are forever."
I also found that light conventionally constructed bullets pushed to 3100 come apart pretty easily when they hit a deer at close range.