I have only shot a 329, but have experienced the difference between grips on that gun, which can only be more pronounced than on a 629.

The wood grips are indeed beautiful, and since I would consider them borderline with Specials out of the 329 it's probably pleasant from the 629. The 329 is unshootable without a 500SW grip with real Magnums, IMHO, but no problem with that grip. When I get a 629, I'm sure I would opt for a rubber grip covering the backstrap if I intended to shoot Magnums out of it.

It's not just the material but how the grip fits your hand. As much as I like my SW I have to say the N-frame grip is not the most comfortable design I have shot, and I feel it focuses more of the recoil impulse into a small spot in the webbing of the hand than other makers' designs. I've never had such an issues with my Taurus guns carrying more rounded grips, for example, which seems to spread the force more broadly into my hand.

Even with the snappy 329, without finger grooves, I have no issues with the gun shifting in my hand between shots. IMHO if you go to rubber you may not need them, but if you really want to stay with wood them may help you hold the gun in position better.