We loaded one for a customer, a Kimber. The rifle shoots very well with our 221g Hammer Hunter. He was able to take a very nice bull in AZ with it last fall.
In my opinion the WSM's are difficult to work with on a short action and still mag feed. Bullets wind up taking up room for powder and good performing powders all need to be compressed with not enough room to get to full potential and powders that are fast enough to fit in the case pressure out too soon. All of the WSM's that we have worked with have shot well but I am less of a fan each time I work one up.
It was a 300WSM that got us started on crimping our loads because the slightly compressed load would not stay seated without the crimp. We now crimp most all loads with very good results. So I can thank the WSM for that.
We have an 8mm barrel on hand waiting for a project. If it were me having the rifle built it would not be a short mag. I would build a 323-338 Lapua imp. or a 323-300 Norma Mag imp. Those two would be fantastic cartridges. The Lapua on the top end and the Norma running near Ultramag type performance but quite a bit shorter. The Norma case is what the WSM wants to be. It has the nice short fat powder column with room to seat bullets long on a standard long action. Fits much better than the RUM. Very impressive round.
If you want to stay factory with the 8mm I would go with the 8mm Remington Mag. Give you a bit better performance without the issues of the short cartridge.
Steve