I want to say that I love my Pure Gold .670 choke. And it shoots very well out of my 870 and Hevi-13 3" 2oz #7's. But I get better 10" numbers with the Rem Ventilator .655 choke with that same load.
I'll show you some patterns.
Pure Gold .670 40yds tape measured 252 shot in 8.5"x11" paper
I think this was the 10" pattern underneath that target above.
Now let me show you some Ventilator .655 patterns.
Now in my honest opinion of shooting these same Hevi-13 3" 2oz #7 loads, I don't think you can hit this much better. This is a 11"x11" target.
Now this was the backside of the cardboard backer that the turkley target above was taped to. There is 282 shot in the 10" cutout.
Now here's another good pattern with the Ventilator and Hevi-13 #6's 1 and 3/4oz load. And that was shot on a cool 45 degree day.