if you can handle a 12ga slug, you can handle a 300win.mag, especially with a good brake.
You DON'T need a 300mag to kill elk, but it's a solid round none the less.
I have a 300win and 340wby and plan to get a 300wsm one day and probably shoot 150/165gr as a lighter weight elk magnum setup....
I also could see using a 270,280ai,30-06 for elk one day as well as a lighter more compact setup.
Savage makes some cheaper rifles that can shoot!
also tikka, browning....
that browning in 300wsm looks pretty nice, with a screw on brake....
300win mag makes me think 180gr bullets, of course you could go lighter or heavier, but with WSM I tend to think more like 150-165-180 than I do with the win.mag.
that .300PRC looks pretty nice I must say.... it has perks that the RUM, wby, etc...don't have, of course it's newer....so it's a maybe gamble...but I could see it lasting.
don't overlook the 280ai, 7mm rem.mag., 300prc, 300wsm, 338win.mag, 340wby.
338win.mag isn't a bad alternative either! shooting 200, 210, 225gr, bigger bullets, but shorter cartridge than the 300win.mag.
I'd strongly suggest a 4-12x to 4-16x scope, anything in there is perfect IMO, I've changed out my 2-7 and 3-9x and even 4-12x in favor of 4-14x and 4-16x.
good luck!