For F class, a number of shooters are looking at the 284 Win juiced up to shoot 180gr Bergers. This is a great ballistic combo if you don't mind the recoil. The 6.5's work very well too. The 300 magnum kick too much.
For Extreme plinking with muzzle brakes, both will do the job very well. The new 208gr Amax has put new life into the 300WM and should be a readily available bullet.
For the 7mm, the 162gr Amax and the 180gr Berger are superb.
I have shot large 30's and 7mm's. All do very well out to a mile+
If competing, look over the rules and see what people are winning with.
For the money, the Savage is the best bang for the buck and I would lean towards the 7RM over the 300WM. I don't like recoil. A savage in either cal has the potential to be a 1/2 MOA rig.
I have seen a 7RM Tikka Varminter shoot 3" and 4" 3rds groups by two shooters on two days out to 1000m. They have the potential to shoot too.
Jerry
PS forgot to mention that the avg lifespan of one of these magnums is under 1500rds. Not so good if you intend to shoot alot. For pure paper punching, a fast twist 223 or 6BR are hard to beat.