The original pre-war Winchester Model 70 in .375 Holland & Holland Magnum had a magazine capacity of 4+1. The currently manufactured ones made by Fabrique Nationale have a magazine capacity of 3+1.
Many of the original pre '64 Winchester Model 70s would experience feeding problems with round nosed soft points right out of the box (unless you smoothed out the feeding ramp with a file). The currently manufactured ones made by Fabrique Nationale feed round nosed soft points more reliably out of the box.
And yes, I have seen a broken firing pin spring on one specimen (just like
@Wyatt Smith). The one I saw which developed this problem, was chambered in .458 Winchester Magnum.
Interestingly enough, I have seen another currently manufactured Fabrique Nationale made Winchester Model 70 (also chambered in .458 Winchester Magnum) which exhibited a most unusual phenomenon:
In order to cycle the bolt, the rifle would have to be brought down to the hip. If one was trying to cycle the bolt while keeping the rifle shouldered, then the action would completely get "Hooked". Considering that the owner of the rifle was my white hunter (and he guides extensively for wild lion), he had very good reason to be concerned.
I honestly think that both actions possess good merit. Although both should be checked by a competent gunsmith prior to being taken to the field.
I personally prefer the original New Haven made pre '64 action. But this is largely due to nostalgia than due to any practical reason.