You’re still cherry picking. Is there a magical line at 1/4 mile where Ballistic Coefficient starts taking effect?
No there is not.
To retain the same velocity at 440yds with a 7mm bullet of the same weight of an equivalent 6.5mm bullet, you have to start the 7mm bullet 50-100fps faster due to the poorer ballistic coefficient. That takes more powder, and more muzzle velocity, resulting in about a 10% bump in recoil for the same on ballistic performance at 1/4 mile. Muzzle velocity is irrelevant unless you’re shooting animals in cages. At every point beyond that, the 7mm is falling further behind. A slight reduction in powder mass/momentum is totally washed away by the velocity delta required at the start to get them to perform the same downrange. This is pedantic at this point, because as you mentioned, they’re BOTH overkill for the intended application. However, the 7mm-08 is slightly more overkill, and comes with measurably increased recoil to accompany that.
There’s just enough sciency sounding stuff here to throw up a smoke screen, so here’s one last attempt to cut through it:
For any bullet you’d fire from a 7mm-08, there’s a ~20gr lighter option that has the same exterior and terminal ballistics with significantly reduced recoil in the 6.5. That includes the 100gr .264 Ballistic Tip, for which there is no equivalent weight 7mm variant.
Cherries do taste better than nits, in my experience, LOL
OP set the parameters he was looking for as low recoil and to reach 300 yards (definitely) and 400 yards (maybe). 400 yards is close enough to a 1/4 mile it makes a nice conversational term.
The 7mm bullet of identical construction to a 6.5 of the same weight, is indeed slowing down faster than the 6.5, and if both are launched at the same speed, it will of course have lower FPS at longer dange. But that is a moot point if both are still going fast enough, and at the ranges stated, both of them will be.
To say "well, there's this 100 grain bullet I could shoot in a 6.5 you don't have an equivalent in 7mm" is the very definition of cherry picking. So, ok, if you wanna limit yourself to a 100 grain bullet to hunt deer, then 6.5 is your huckleberry (but a 243 would be even better at that).
For any given bullet weight, you can launch a 7mm at any given FPS for less powder and recoil than a 6.5 - and it does not matter what 6.5 it is (CM, 55, PRC, etc), physics favors the larger bore size in terms of bullet weight X + powder charge Y = Z FPS.
Note, it's also true the bigger you go - a 130 grain 308 bullet can be kicked out at the same ish velocity as a 130 7mm or 130 6.5 for even less recoil. But none of the 130 class 308 bullets I am aware of can keep the velocity needed at 400 yards, where there are some 7mms that can, so 7mm-08 is a solid choice for OPs stated criteria.