I have a 3" 629 which the Performance Center had double-Magnaported (4 ports). I also have a 4" 29. Relying on faulty memory, for years I was under the impression that they recoiled similarly. However, I finally got around to testing them side by side, the 29 with the Pachmayr Presentation SN-S grips which have always been the only acceptable interface between me and a SB N frame, and a custom (Fishpaw) checkered walnut copy of Pachmayr Compac Professional grips (only thicker, almost the same circumference as Compacs) on the RB 629. In other words, for me, probably the best possible grips on each revolver.
With full power .44 Mag ammo, the 3"629 was significantly less recoil, both up (seen) and back (felt). Definitely a worthwhile improvement, although I consider myself restricted to jacketed ammo for the 629.