Looks like you made a decision but the good ol 6.5x55 Swede or the AI version might fit the bill. In between the 6.5 CM and 6.5-06 with pretty readily available components.
Ah, I sound like I've made my mind up,, but I'm easily influenced!
I've attached my spreadsheet analysis of various cartridges. The 6.5x55 Swede seems a bit on the slow side but I do really like the idea of the 6.5-06, 6.5-284 and the .25-06 Rem.
These three would allow me to use the long action I have already and not swap out magazines. They have great velocity numbers that fit my goals and recoil is very managable. Especially once suppressed and weight is likely to be more like 8.5-9 instead of 8 which this analysis is based on. Sadly the .25-06 is out because DRT doesn't make bullets in that caliber.
So the decision really comes down to if I truly want to embrace and try-out the Rokslide / Form path of "low-recoil makes shooters not suck." If so, it seems that the 6mm CM is the obvious choice.
In terms of determining which cartridges have the longest lasting barrel life, John Barsness has a formula he proposes in his book "Obsessions of a Rifle Looney." (As an aside, I'd highly recommend all of his books to anyone who likes this stuff enough to have read this post!)
His formula is Caliber's Cross Sectional Area divided by Case Capacity.
He says,
"Cartridges with a bore/case ratio of under 10 tend to be rough on barrels, and kick noticeably harder. .....Get down around 8 and they really start to eat barrels, and buck like rodeo bulls. A bore/case ratio much above 10 results in cartridges noted for high efficiency, particularly long bore life and relatively light recoil for their ballistic results."
For ease of calculation here is the cross sectional area of various standard calibers:
6 mm/ .243- .0464
6.5 mm/ .260- .0547
270- .0602
7mm/.280- .0633
.308- .0745
I've added this column to my spreadsheet. The comparision from a barrel life basis for the cartridges being considered goes as follows: 6.5-06 (shortest barrel life), then 6.5-284, then 6 CM, then 260 REM.
Because I'm enjoying this pretty useless exercise, I want to find a reliable way to calculate and populate the last column of this spreadsheet before making a final decision. That is barrel life and inherent accuracy. Still working on how to populate these with good data so help a guy out!