Given the closer ranges you will be bunting, I'd go with the rifle that you have the greatest confidence , and gets you on target the fastest. At 100 yards, there is a good chance that a smart, old Mulie(or another nearby deer) may be aware of your presence With the right bullet that will penetrate from an angle, either set-up will be effective on mule deer for more then twice the distance your quide has advised, and I would be prepared for that possibility. My personal preference would be the 6.8. Most all my mule deer taken with 6.5's and 270's from 100-700 yards.