I'm not sure I'd be "starting" at the 300 mags for an elk rifle, not really needed.
While there is no question that the various 300's and 338's work great for elk, there are lots of smaller calibers that work just fine and are much more user friendlyh.
I hunted almost exclusively with a 30/06 for the first 15 years I hunted and killed a lot of game with one, including a dozen elk or so. It worked great. I later switched to a 338 and killed 14 elk with it, but I've largely quit hunting with it. I just dont like shooting 300's and 338's that much anymore. I can still shoot them well, just prefer rifles that are more pleasant to shoot.
The last 15 or so elk I've shot have been with a 7 RM, which I find more pleasant to shoot than the 300's and 338's.
I'm downsizing again this year and will be shooting a bunch of elk in the future with a 7-08.
I still think the 243's are a bit on the light side (although I've shot a couple elk with them), but anything in the .25, .264, .270, .284 range will work just fine. No reason to only look at the magnums in those calibers either, the standards are more than adequate.
The 3 most important things to killing elk are shot placement, shot placement, and shot placement...roughly in that order. A distant second would be bullet construction.
I'd much rather hunt with a lighter rifle I shoot well, than to hunt with a 300 mag that I didnt really care to shoot. Accuracy and range time trump headstamps...all day long.