Leave out any of the cartridges with "magnum": in their name and you are good to go. Magnums are not needed because they cost more, wear faster, and offer minimal ballistics advantages.
Actually, the .25 WSSM and .257 Weatherby Magnum make excellent choices for low volume varminting/deer rifles. Emphasis on “low volume” – if higher volume is required a centerfire .22 is called for. Granted, the .25WSSM, and less so the .257 Weatherby, have issues such as ammo cost and availability, but those are of no more concern to the handloader than is the pitiful variety of factory ammo for the .257 Roberts. As a handloader, my .257 Roberts is easily my favorite rifle and is used to hunt prairie dogs to deer and elk. While I don’t care for the WSSM in any caliber, I would not hesitate to use a .257 Weatherby in place of the Roberts.
"Long range, flat shooting" is not a good excuse for "oh, i don't know how to aim and shoot at that distance".
True, but “flat shooting” often translates to less wind drift as well. Adjusting for drop and holding on point is easy, adjusting for wind is much more difficult.
You make the argument below that “hunters don't shoot past 200-300 yards”, which is nonsense to a lot of varminters. If you’re not willing to shoot further in a prairie dog town you can run out of targets fast. I’ve taken between 75 and 77 coyotes and many of them have been between 300 and 500 yards.
Besides, i stand firm in my belief that hunters don't shoot past 200-300 yards. Snipers do.
That may be your belief, but as you say below, you don’t do much elk hunting and I’m willing to bet you’re not hunting mule deer in open sage, either. I’d also guess you’re not doing much antelope hunting, either, especially on public lands that see a lot of pressure. While “getting closer” is nice when you can do it, there are many reasons totally unrelated to the hunter’s skill that can prevent a hunter from doing so.
My most difficult hunt to date involved a herd of elk we spotted at 600 yards about 11:30 AM. We got as close as we could, about 450 yards, fairly quickly. “Getting closer” required sitting through rain and snow storms and then crawling the last hundred yards head first on my back, through sage and cactus. I was finally able to take a 350 yard shot just before the end of legal shooting hours some six hours after we first spotted the elk. These days I am prepared to take shots out to 600 yards, depending on the rifle in hand, and practice on clay pigeons out to that range. The last coyote I took was head shot at over 480 yards.
6mm Remington is my do everything rifle (everything except bison, moose, elk, and bears, which i don't usually hunt). I just use different bullets for different game. With the 100 grain round nose bullets i would not be shy of shooting elk.
However, all of these on the list are intense and hot calibers. If one wants to take more than 3 shots, they would do better with a heavy barell.
Dual purpose cartridges are rarely used for high-volume varminting. If high-volume varminting is the goal a centerfire .22 is indicated.
By the way, I starred hunting elk in 1982 and have only missed 2 years since then. During that time I’ve seen more elk wounded with .243 Win (another 6mm) than all other cartridges combined. My .257 Roberts and 120g A-Frames don’t come out until after my first elk is down and I’m focused on deer.