Brent,
Scopes can do all sorts of weird things--including erratically going from one POI to another between strings of shots. They can also start stringing shots horizontally, as in the second group. The mounts themselves may even be involved.
Your theory is based on assumptions about bullet stability that are wrong. Yes, it's coommonly believed that bullet stability declines at longer ranges, but I already outlined the reasons that isn't happening here. You just refuse to believe them, even though they've been proven over and over again.
Plus, if bullet stability were the problem, both groups would have fliers in all directions, instead of being basically strung out horizontally.
As jwp pointed out, marginal bullet stability is definitely not the problem here, and just because you've induced it with too-long bullets in your rifles doesn't change that. A 1-10 twist in a .300 Savage will stabilize a 200-grain spitzer started at 2200 fps.
