I have no experience with the 8mm.... yet, but with 7.62x54r there are a few variables.
First it depends on the rifle doing the shooting. my m39 prefers heavier gr. weights and really does not shoot the cheap czech silvertip stuff well at all. the hungarian heavyball on the other hand has produced 2.5" groups @ 100 yards with just the iron sights. i've heard that the czech stuff works very well in m38 and m44's.
Second, country of origin can come into play. some use different bullet designs (finnish 7.62x54), some use different materials (many steel cased, but some (yugo) have brass), etc.
My solution in progress is to get samples of each over time and try them all. When I am satisfied I've found the best I'll buy a bunch of it.
There are also available in both x54 and 8mm new commercial loadings from S&B, Wolf, Igman, PRVI and some others.