I have the same gun.
After asking the guys here at OG, I went with the Hevi-Shot choke tube (.664)
I patterned using H-13, 3.5", #6 shot. At 45 yds I had around 220 in a 9" circle. And 38 in the head and neck area. I also shot at 28 yds, and could not count the pellets because the head area was missing from the target.
I also bought a box of H-13 #7, a few days ago. But have not shot those yet.
My season is two weeks away, can't wait!