.670 is a choke I've never tried. the tightest one I own is .675, so maybe a few folks with your choke will chime in. The Jellyhead throw a nice even pattern for me, but I get higher numbers out of others. I really think the 835 perform their best with heavy payloads.
If you do a deep cleaning and still are not happy, you might want to try a more open choke. With the 3.5 Heavy 7's I get 250 - 275.
