I've had #'s from 165 to 210 with the 3" Magblends out of my 870s. The IC .665 was the only one to break 200 in 10" at 40 yards for me. I haven't tried the Jellyhead .660, but I've heard that will do it easily, I'm assuming because of the all the 6s and 7s in the load. However, I'm not looking to go any tighter. I shoot 95% of my birds at 30 yrds or less, so I prefer a pattern, not a slug.
In your case of getting around 150 at 41 yds, you might just need to go a bit tighter like the Jellyhead .660 or Hevishot choke. Of course you could get a custom choke much tighter than that if range is the issue.