I built a 6.5 SAUM to shoot deer with the 140s out to 1000 yards while maintaining at least 1000 ft*lbs of energy. I owned a 7 RM and shoot the 168s and loved that combo. I sold the 7 RM but ever since, I wanted a 7 SAUM to shoot the 168s. I could hunt elk with confidence using the 156s, but its on the lighter end for longer range elk projectiles. I have more dedicated LR elk guns to choose from anyways.
For your choice, bullet weight is the only thing different. If you like heavier bullets, go the 7.