The roller cam option is a very expensive conversion; over $150.00 in parts alone. The roller should have only a limited impact on the weight of pull because the main factor in the weight of pull are the mainspring and slide rebound spring. Regardless of how smooth you make an action, you still have the resistance of those springs. I've never heard of a 3.5lb DAO trigger on a revolver...but I'd sure be interested in seeing one.
A good action job on a S&W should run around $100.00. Generally, you can take 2-3lbs off the trigger pull weight, and make improvements to the smoothness and consistency of the pull.
Changing to DAO has no impact on the feel of the trigger whatsoever.
