I started to chim in and say the .300RUM, even though I shoot the 7mmRM. However, I went to the Ballistic's Program right at the top of this Forum thread (Bullets, Barrels and Ballistics) entered the required basic info and came up with suprising results.
I used info from Noslers 5th edition. I used the 150gn Ballistic Tip for the 7mmRem Mag., with BC of .493 clicking along at 3248fps. This is acheived with 63.0gn of IMR4350. Zeroed at 300yds, bullet is 23.1" low at 500yds (4.4MOA) and 218.0" low at 1K (20.8MOA).
The 180gn Ballistic Tip was used for the .300RUM. It has a BC of .507 and clicks along at 3229fps. This feat took 89.0gn of IMR7828. Zeroed at 300yds, bullet is 23.1" low at 500yds (4.4MOA) and 216.3" low at 1K (20.7MOA).
The 7Mag 150gn gets to 500yds in .549 seconds, traveling 2305fps with 1769.8ft/lbs. At 1k (1.344 sec), 1551fps and 801ft/lbs.
The 300RUM 180gn gets to 500yds in .549 seconds, traveling 2313fps with 2138.7ft/lbs. At 1k (1.337 sec), 1575fps and 991ft/lbs.
Go with the 7Mag. You'll get the performance you need, less recoil and 33 more bullets per lb of powder. JohnnyK.
"The only thing necessay for the triumph of evil is for good men to do nothing."