Just some thoughts for consideration...
OK Rich I've apparently painted myself into a corner. Apparently EOL and Berger are moving forward with a 155 grain 6.5 bullet.
Bob Cautericio has been making a 155 grain VLD for a few years now. I've been shooting them for at least 4 years that I can account for. Litz has even done his 'evaluation' of these bullets.
I suggest finding and reading the evaluations of the Berger version first before jumping into a project to go longer and heavier with mono-metallics. Then use a real program to establish stability factors and twist rates.
There is a problem with powder selection for cases with large capacity and shooting small diameter bullets. The bigger the case capacity and the smaller the bullet diameter, the slower the powder has to be. There are diminishing returns here since these ultra-slow powders require longer barrels. You can compromise by using less than full cases and shorter barrels but then the answer becomes, use a smaller capacity cartridge.
There are actions available for the larger rim cartridges such as the Lapua and even the Chey-Tac if you really want to go over board.
Surgeon makes the XL - $1785.00
Badger Ordnance makes the M2013 - $1385.00
Barnard makes the PLM - $1500.00
There are a couple of others but these are the ones I use. They are all well made and over-built, not clones of an oversized Remington M700. The Surgeon includes DBM bottom metal but single shots are available.
Another consideration would be to design a bore rider bullet but you would need to give design consideration to the chamber and resulting longer 'free bore'.
Enjoy the process!