I don't know anything about the new vs old magazine box differences but Ruger's short action is longer than Remington's and does allows longer OAL. As far as bullet weights go run the numbers and load them up and see what you get. When the 35Whelen, 358Win, and the 350RM came out (obviously not at the same time) bullet choices were a lot more limited. When Remington commercialized the then wildcat 35Whelen bullet choice started to get better. An old favorite was the 220gr Speer which was and still is a good bullet on game but it suffers in the BC department and contributed to the "woods caliber" perception. So did the 250gr bullets of the day that were pretty much all roundnoses. That and the assumption of "heavy" recoil based on a mental comparison w/ 30 caliber, read 308/30-06 recoil kind of sealed the fate of these cartridges as far as popularity. Now don't get me wrong, if you load up one of those Remington carbines in 350RM to full house levels w/ 250gr bullets you will notice the recoil. Magazine articles on the 350RM when it was introduced always spoke to considerable recoil in those lightweight carbines and that didn't help sales either along with the unconventional appearance of those rifles. But I personally don't believe that the 250s give any real advantage over the useable range with any of these cartridges, especially with the 358. Look at the drop and energy numbers with realistic velocities and then do some meaningful penetration/expansion testing with any or all three of these cartridges and decide for yourself. You can get some pretty decent velocities with the 200 grainers but again the BC's of those bullets work against you and you'll give up some penetration. In my opinion lighter bullets have no real purpose in these calibers except maybe plinking loads, but you will definitely have to re-zero. Some of the newer 250s have good BCs but you generally can't push them fast enough to have any advantage downrange over the 225 spitzers which turn out to have pretty good BC numbers. When I started loading for the 358 I initially used Hornady 200gr spitzers primarily out of concern of what recoil would be in a relatively light rifle. I quickly moved up to 225s and that is all I load now. Sierras for practice and whitetails and Partitions for anything heavier and that is a purely cost/confidence decision. Based on my experience the 225gr Sierras are enough bullet but if I'm spending a bunch of money on a moose hunt I'll use the Partitions just because they give me more confidence. I still have a bunch of those 200gr Hornady loads and they are awesome on whitetails but they don't really offer any advantage over the 225s except slightly less recoil. Hardly noticeable to me but recoil is subjective and everyone has there own opinion. The real issue to me with switching bullet weights is the POI change. Make sure you re-zero if you are hunting with different bullet weights. I have my rifle zeroed w/ the 225s just under 3" high at 100yds which puts them right on at about 225yds and a midrange max of 3" inches. With that zero the 200gr loads are a little bit less than 1" high at 100yds. If you were zeroed 2" high at 100yds with the 200s (which is a pretty good zero for that bullet weight btw, the 225s midrange trajectory would run about 5" or maybe a bit more, too much for my taste.
When it comes to the newer premium bullets, I just don't see the need. The Accubonds are good bullets and generally a bit less expensive than Partitions but OAL becomes an issue w/ at least some if not most of the the short actions. Look at Nosler's BC numbers for the 225 Accubond vs the 225 Partition and you might be surprised. I was, the Partition is slightly higher so the only advantage to me would be the slight cost difference. The "X" bullets will have the same OAL issues, cost a lot more and I am not convinced that they will kill any better than a Partition. So for whatever it's worth, that's my opinion.