An RSM is also a magnum action. Both are discontinued. I personally prefer the Ruger for hard to defend reasons, mostly I just like them and have a collection of them. Most of the RSM stocks are fantastic being Circasian Walnut. To get quality wood in a CZ you need to find a real premium one or an aftermarket such as the upgraded wood on an AHR. If you want a synthetic stock, go with a CZ... it is sacrilege to put such a soulless appendage on a RSM.
The RSM looks like a much higher end gun that at the price it sold for new, Ruger lost hundreds of dollars each. It has an integral quarter rib that is machined as part of the barrel rather than added on. Very unique to a rifle in that price range or even at triple the price.
There is a slight flaw in the Ruger reciever mounted safety. So if you plan to be cycling the bolt whilst being mauled by a buffalo, the CZ may have an advantage
Both are big rifles made to handle recoil. If you go with a Ruger, be sure to check the torque on the large angle screw and don't over tighten the others. And keep the factory rings together as they come packaged. The rings are machined as a set. Read the couple of relevant pages in the book! Most of any issues people have with Ruger Mark II or Hawkeye rifles could be avoided by understanding how they are designed or by simply following the simple instructions included with them. They are NOT designed like a Winchester. They do NOT need to be bedded or anything other than properly torqued screws.
If you go with a CZ, either throughly check the rifle for feeding issues or plan to have it worked by a competent gunsmith. Although there should be less issues with a 375 than a 416 Rigby or even a 458 Lott.
Especially some of the older RSM models feel a bit front heavy, essentially the 780 serial prefix models. I prefer the 750 series.
I for one like the Ruger scope rings just fine, they really are a sort of QD mounts.. Many prefer the Alaska Arms version of QD mounts, I suspect simply because of the idea that a QD mount should have a lever. If you can find them, Warn QD mounts are outstanding for a CZ. The factory scope rings that come with a CZ seem flimsy for a magnum caliber.