I broke down and bought Hevi-13 loads for my new 535. I'm shooting the 3" 7's out of an Indian Creek choke tube and the results are phenomenal!
I'm not sure, but I'm guessing the results are more from the shells than the choke tube. It doesn't shoot lead all that well, but the Hevi's are awesome.
I think Environ-Metal (makers of the Hevi-Shot) is still giving $5 rebates on boxes of shells purchased until May. You can find the coupon on the Hevi-Shot website if you're interested. Just remember, your choke has to be rated for 'heavier than lead' to use those loads.
rw