Back to your 6" groups. My scoped optima is a little over an inch@ 100 off bags with Blackhorn powder@ 85 gr wt and 250 Barnes TEZ or TC cheapshots. We tried pellets in my daughter's Wolf and shots were all over the place even at 50 Yds. Went to grain powder, 45gr wt., and groups tightened up for her.
Also, you mention you are 7 foot tall. I don't know how experienced you are with shooting, but your rifle probably doesn't fit you. How is your cheek weld? Do you have to reach or back off to get your scope in your eye?
Edit to add: Since you are new to this MZ stuff I listed my powder in Weight, most will use Volume.