Between the calibers you mentioned, I like the 6.5/Gibbs made on the 270 or 280 length case and Norma brass. Have two of them, at present and they perform very well. There is fireforming envolved in any improved case.
The smith that chambers more Gibbs cartridges then anyone I know is Ray Romain in Brockport, PA. 814-265-1948
He will answer any question you may have.