I've owned a couple 629's in my day, but none of the exact models you're talking about...
What do you want it for? Longer barrels for hunting and silhouette, 4" if you ever think you'll want it on your hip.
A full underlug 6.5" Classic isn't bad to shoot at all. The 4" is obviously going to bark more... Still, I'm not crazy about the V-Comp.