What is the weight of the two models? Mtn Gun, 39 ounces, 4" Std bbl, 41 ounces. Both wear Hogue grips.

Is there an accuracy advantage of the heavy barrel? I have found no difference in accuracy between all my 4" 629's but the Std bbl does have less perceived recoil with all loads. My favorite is the Mtn Gun because of the light trigger pull it has due to an 11 lb Wolff rebound slide spring, and the Patridge front sight I installed. For carry tho, I prefer the 329PD.
At 26 ounces,plus ammo, there is a world of difference between it and the Mtn Gun on the hip!
From what you've written,my suggestion would be to go with the Std bbl and install a lighter RSS if you desire a lighter trigger. You'll never notice the difference between the Mtn Gun and the std bbl on the hip.