Conversations may evolve, but going off topic and introducing something not asked about isn't.
I built a 6.8, but in the process of researching it over two years, the one thing that stood out were all the fanboys of another cartridge intruding into conversations and insisting their's was the only answer. It didn't help the OP whatsoever, it just diverted the topic and they become flamefests of ego.
As for the 6.5G, it got it's creds shooting and earning the 600m record which it held for some years. I question the background of a 6.5 fan who doesn't know this. After all, it was developed by the creator of the PPC cartridge, all of which were designed to garner long distance precision shooting records - on and in paper.
Let's get back to the topic, which is really about 6.5G being "as good as" .308. Again, study the ballistics - and use a jaded eye, because most of the data out there isn't directly comparable. Some judicious thinking is involved, loads can't be identical, and barrel lenghts alone are usually out of the norm. 26" isn't common in gun racks.
The significant difference is that a 123gr bullet propelled by less than 30gr of powder cannot and will not perform equally with a 162gr bullet pushed by 50gr. Ballistic coefficients in the respective bullets are about equal, so the bigger heavier bullet will retain more energy longer.
It's been the basic thesis of some 6.5G enthusiasts to beat the drum that their chosen One Bullet To Rule Them All can replace the .308. Somewhat silly when the originator and developers never promised it.