I'm going to put my thought into this. I don't have a .45-2-7/8 but I had a .45-3-1/4 about the same just a little more powder and it shot very well.

and I have shot the 7/8 that friends have asked me to shoot many times and they all shot well.
I also have a .50-2.5 and out of all the Shiloh's I have in different calibers I favored the .50 above all for many years and the rifle shows use. A few dents in the wood and most of the bluing is wore down to bare metal. The wash board tool marks in the bore are all wore off and the bore looks like it was hand lapped after more then 20K rounds shot through that rifle and it still shoots. I will say it shoots better now then when it was new.
But it's not a caliber for the recoil sensitive shooter. Neither is a 2-7/8.
In my opinion for a all around rifle like hunting or clanging iron both calibers are more then needed other then the wow factor if one likes to impress the .22 and .308 caliber shooters at the range.
As I age I have been down sizing my calibers even to a .40-65 for the last rifle and it sure is a lot of fun to shoot and the .44-77 for a hunting rifle that gets the job done also in fine shape.
I think the .45-90 is about as good a caliber for all long range shooting iron or paper as well as for hunting, but all of this is the choice of the shooter.
I think at my age of 78 that I may be getting a little wimpy and going to the fun calibers but I still like my .50 and still like shooting it.
Down the line you will have both the .50 and the 2-7/8