The really difficult part of discussing the differences between 6.8 and 6.5 is that they are relatively minor. They are both improvements over 5.56 in many ways. Not all the improvements are in the same area. What is difficult for some to accept is that some areas can't and will not be comparable. Two different calibers, with different case shapes, different bullets, and different end goals, can't and won't be the same.
If there is a problem with discussing those differences, it's that some won't accept anything less than compete acceptance of all the data they publish. To even question their perspective automatically means being completely in the koolaid camp of the opposition. From that perspective, only one caliber can be right, the other must be wrong, and the natural order of the universe will right itself.
Far from being a disciple of the 6.8, I stumbled on it looking for an alternative to the 5.56. The state of Missouri had already accepted it as a legal method to hunt deer - in fact, now allow any - ANY - centerfire rifle cartridge. I don't accept the 5.56 as a viable hunting round. Being an old .308 fanboy, it just didn't make the grade regardless of my 22 years Reserve duty.
Once I looked at the origins of 6.8, I ran across the 6.5. Another alternative. Research into that showed a different origin, and different design parameters. If anything, I just repeat what the proponents and their websites say. That has become a moving target lately - and even the owner of one caliber now insists that the history of the cartridge is quite different from the published web page on his own site.
What is really going on is a marketing challenge to confront the 6.8 - which has become accepted by a growing number of AR owners who want to hunt with a legal round in their state. Through circumstances entirely within their control, in my opinion, the 6.5 has not prospered. Whether this remains true now that there is a new marketing effort by a second party is up in the air. Another AR caliber to choose from isn't a win/lose proposition for shooters - it's all good as it will improve sales for all makers, and offer more for shooters. What is a win/lose is to make it that kind of contest. Nobody has to pick just one - an AR owner can have both. My attempt in discussing the difference is to amplify what each does best. If this is perceived as being a wholesale sellout to one side is a good illustration of how much some parties in the 6.5 camp are insistent that only they can be right. That attitude is not constructive to the discussion, or for AR fans.
I've never said the 6.5 was inferior in all but one respect to the 6.8, others have. I haven't published manipulated data based on one barrel length asserting it as another, and I haven't insisted that only one can be right - and only the competent can agree with me. I haven't said I'm expert on the subject. I have said what I know to be fact - and if that is difficult for some to admit, the problem isn't with me. Check other sources. Research it. Be open and find out for yourself.
I do, I don't accept just one view as being the end-all be-all on a subject. I certainly don't have expectations that one caliber can solve all problems, can be the only proper selection by the Army, or that their even needs to be change. Having a contrary opinion isn't valid grounds to be negatively characterized - unless someone is getting down to their last desperate bid opposing a valid opinion, one they are afraid is actually fair and well informed.
I do welcome others to read other forums. Find out for yourself, choose what is important to you, and try it. If it doesn't work, fine, if it does, ok. You found out for yourself. After all, if we didn't try something new, we'd still be shooting blackpowder.
Both parties are looking to improve on the performance of the 5.56. How that is done may well be superceded by an entirely different caliber yet to be introduced. It's happened before, it could happen again. It doesn't mean either the 6.8 or 6.5 is going away any time soon. That would also be a contradiction of historical precedent.
