I think it should be a 280 or a 280 AI with a 24 inch barrel and a 1 in 8 twist. I would advise the regular 280 which buyers could easily convert to the AI version if they so desire.
This would cover most of the same ground that could be covered by a fast twist 270,a 284,or a 7mm Remington magnum,but would require no changes other than the barrel and would require no additional special tooling or investment. They could paint the stock a custom color,and it would be good to go.
