SHORTFUSE,
I havn't shot the 642, but I have a hard time imagining 3oz making that much of a difference in recoil. Weight is just one of several factors where recoil is concerned. Design of the frame, Style of grips, powder charge and bullet weight are others. As the 342 and 642 are otherwise identical except for weight, I think the recoil differences will be slight.
Bottom line: both guns give a healthy kick. One just kicks a little tiny bit more. If you think the 342 might be too much for you, then the 642 probably is as well. If it we're my decision, the extra $100 the titanium model runs would be more of a factor than the recoil. Hope this helps, good luck!