6.5 mm Grendel vs 6.8 mm SPC

It seems nowadays (for last few years) on all gun forums and blogs there is a never ending discussion about which one is better (as a "replacement" for 5.56NATO): 6.5 mm Grendel or 6.8 mm SPC. You can hear all sorts of arguments some of which do make me wonder...

Imho some points should be obviuos (without talking about any long rance balistic testing and without having any battle wounds or black belt in terminal balistics etc) just by using logic. So, assuming everything is (more or less) equal:

Grendel is designed for longer bullets than SPC using same OAL cartridges.
Then, if bullets are of equal weight and design, 6.5 mm bullets will be longer than 6.8 mm. From this follows, that (again, assuming the same design) 6.5mm bullet will have better BC. This means it will have better long range ballistics. That's with the same weight bullets. But, as said, Grendel is designed for longer bullets - that means it could use even heavier (longer) bullets, which have even better BC (assuming same design).

Talking about terminal ballistics, (again - assuming the same bullet design) 6.5 mm of the same weight should have better penetration characteristics than 6.8 mm (and even better if heavier) because oh higher sectional density. If we have the bullets of terminally stable penetrator (shoulder stabilized) design 6.8 mm should be slightly more effective, because it has cross-section ~9.5% bigger than 6.5 mm (both ought to have enough energy to fully penetrate through human adversary). Using hunting type expanding bullets the difference should probably remain (although, because of bigger bullet length and weight 6.5 mm could expand (proportionally) more). Then, using disbalanced (tumbling) bullets, which are typical for military ammunition, 6.5 mm should (might :) ) be less stable terminally than 6.8 mm bullet (of the same weight and design), because of the greater length. Then, when it tumbles it should be somewhat more effective, because (again, asuming the same mass and design) of the greater lenght. And because of the longer bullet it will have higher side loadings and should be more likely to fragment...

No rocket science here, really.
All the turmoil ensues only when you start comparing apples to oranges: different bullet weights, bullet designs available in one caliber but not in another etc etc etc...