I had a STW but sold it, have a 7mm Rem Mag and have had many over the years, also have a 7mm Wby and I also have a 7mm Allen Magnum.
This is Long Range Hunting. Now, if your definition of long is 600-700 yards or less, and if the factory ammo thing worries you, and if money might be a problem then I'd say go with the factory setups. When is the last time that any of you have had to not hunt with a wildcat because you couldn't find factory ammo? I've been loading for longer than most can imagine and have never had my ammo supply become a problem. Planning helps a lot.
If you want the best performance you can get at loooong ranges them the 7mm Allen Mag is the winner hands down.
The 7mm AM has been the easiest 7mm to work up a load for that I've ever worked with. I've found nothing picky about it and had far more problems finding a load for one 7mm RM that I had.
There are no "special dies" needed for the 7mm AM. You simply buy a set from Kirby just like you'd buy a set for an STW or any other gun.
I believe that I have in my 7mm AM the best long range 7mm available. I spend far more time hunting and shooting with this gun than with any factory gun I've ever had. Months to find the right load for my 7mm AM......nope, sorry. Simple and easy and no matter what bullet weight I try it likes them from 160s up to 200s.
I read a lot about the AMs being bound by one bullet or picky to load or time consuming but I find it to be the opposite.
I'm not knocking the factory rounds. If that's you piece of cake then cut it and eat it. If you want the absolute best long range 7mm then for me it's the 7mm AM. I guess in the end it might also come down to money as building a 7mm AM is probably going to cost you more than buying a factory gun. But remember, if you start putting money in the factory gun, where and when do you stop and how much can you spend to be cost effective by using the factory over custom or semi custom?
Just my $ .02 worth. Take it for what it's worth.
However it kinda looks like, other than Kirby, my opinion was the only one that included experience with both rounds mentioned. Even if you go with the STW you will be very pleased and it is capable of killing game at long ranges.