I have two Mauser 98 one is still a 8x57 Danzig made, the other is now reamed out to 8mm-06! Both shoot really well with 200gn bullets
I've built a couple of 8mm-06 rifles for folks and one for myself, using a 30-06 reamer, then an 8mm neck/throat reamer. All were done on take off milsurp barrels, other than the one I built for myself, which was done on a military NOS replacement barrel, still in the wrap.
I like the cartridge a lot, but I like the 338-06/35 Whelan more and the velocity advantage over the 8x57js, when loaded to 50K psi, isn't enough to worry about in the field, so I sold it to another fellow who had been thinking of getting one built.
Back when I made up those rifles, finding 8mm barrels, without importing from Europe or placing a "special order" in North America was not easy.
We utilized what we could find and at that time, 8x57jx chambered take off barrels were in almost every LGS that offered gunsmithing services, many of them in excellent condition and they were mostly taking up space, and the smiths sold them off very cheap.
One of the biggest mistakes (IMHO) made by smiths back in the day, was to "reprofile" these barrels to make them more presentable, or try to duplicate the esthetics of a commercial barrel.
This was not conducive to accuracy, no matter how well the job was done.
German engineers went to a lot of trouble to figure out the best barrel profiles to provide consistent harmonics with issue ammunition. Those barrels almost always will have "tooling" marks under the covered areas and some will have them all the way to the muzzle. Some folks find this unsightly.
When I do builds using these barrels, I remove the military style sights, chuck them up in the lathe and polish away the tooling marks, nothing else. This just makes life so much easier when working up loads later.
I have seen a few reprofiled barrels shoot well, but only a few, most don't or are extremely fussy about which load will shoot acceptably and it's almost impossible to find commercial offerings that will do the job.