.280 Enfield...Ahead of its time

[stanc]

They tested 6.35mm and 6.8mm, and found that these two clearly performed better than 5.56mm, 6mm or 7.62mm, taking a wide range of metrics into consideration. So it's safe to assume that 6.5mm would perform very well too.

Probably so. But, without knowing what their metrics were, or for that matter, any specifics (bullet weights, muzzle velocities, etc) I'd prefer to not assume anything about the claimed conclusions. They might be valid, or they might be a case of GIGO.