No flies on the 300Win Mag IMHO for a lot of reasons. Especially easy availability of a very wide range of components and very good performance.
It isn't my first choice, especially on such a light platform but that is just a personal preference and low tolerance for recoil.
Guntech set up an excellent base for this platform but I would also suggest that you also pick up your own reamer which has been manufactured to minimum specs. This might not guarantee tack driving accuracy but it will certainly go a long way to getting there. Also, the neck diameter on the reamer should be machined to the median diameter between minimum and maximum specs. I have seen 300WM cartridges stick at the most improper time because the case necks were on the large side. Not often, but it happens. Also, if you have done your own due diligence and know which bullet you want to use, have the leade cut on the reamer as well for that bullet weight, shape length. You will be able to load other bullets to the sweet spot but they will either take up a bit of powder capacity because they have to be seated deeper or loaded further from the leade giving you a bit of free bore. Whatever, the 300WM is a proven performer with lots of powder capacity to fill 99% of your needs.
If you are going to reload, this reamer can be used to cut a custom forming die as well.