I find 30 degree shoulder cases still need to be trimmed a bit. 40 degree cases can go a lot of firings without trimming in my experience. Technically, when you have to trim the brass is flowing out of somewhere in the case. That means you would likely get more case life out of a chamber with a sharper shoulder angle. Unless you shoot A LOT you will not notice in reality.
Looking at the saami chamber dimensions, the 243 Winchester has about a 0.0160" freebore. That is plenty to get the base of the bullet out of the case, typically. If it is not you could run into donut issues depending on how you size brass. The truth is, the freebore on saami 6 creed is slightly less from quick math, so you would have the same situation with the same bullets. Both have a 1.5 degree leade angle, which is typically what is accepted as the best for accuracy.
The last thing is mag length. If you want to load close to the lands in an aics mag you will be pushing it. A non-binder plate mag will solve this issue.
If you plan to Ackley improve as many have suggested, it is not a simple matter of running a reamer in. To make the fireforming work as designed, the barrel must be set back to create a slight crush fit on virgin 243 brass. If all that is done is chase the chamber with the Ackley reamer, you will need a hard jamb or a false shoulder for fireforming. That really isn't a huge deal as long as you are aware and comfortable with that process. Fireforming brass in a long chamber with no way to keep the case head against the bolt face COULD result in much shorter brass life or even failure.
Those are the idiosyncratic differences. In practical application, the only real difference is factory ammo availability.