I'm going to shoot my 535 tomorrow with an Indian Creek .660 and a SSX .643 with Hevi #7's.  Mine also has a 20" barrel.  I will post my results.  I'm shooting the 3.5" 2 1/4 ounce loads, but it should give you somewhat of an idea if you're shooting 3".  I have some various Winchester Supreme shells that I'll use for making sure I'm hitting where I want, and I can throw a couple of those downrange to give you lead numbers also.