Depending on load, you'll gain 50-200 fps going from a 3" barrel to a 4" barrel. If you're worried about a potential angry grizzly or moose, ammunition selection (hardcast or a bonded hunting bullet is ideal) is likely to be your most important gear decision. A lot of .357 defensive JHP have shallower penetration than you'd want for a large animal. Still, that extra velocity is nothing to dismiss out of hand.
Red dot upsides:
-Easier for older eyes to see, especially in poor lighting conditions.
-Sighting system is on the same focal plane as your threat.
-Sight window can function as a big ghost ring at very close distances if necessary due to dead battery, cracked window, blocked emitter.
-Potentially easier to zero for a wide variety of loads.
Red dot downsides:
-Needs batteries.
-Requires practice to find dot quickly; otherwise, can be slower than irons.
-Potentially less weatherproof, especially open emitter designs.
-Can be less durable, depending upon optic and mounting choice and iron sight comparison.
-Cost of quality optic and mount.
-Unlikely to have backup irons on a revolver.
If you don't think that you'll put in the reps necessary to make the a red dot optic work for you, you might like the sights that LPA offers. They have adjustable rears with or without fiber optics, and front fiber optic sights. You'll need to order the correct front sight option for whatever revolver you get (pinned or DX style). You could theoretically pair one of their rears with a tritium front.
Meprolight also offers tritium sight sets for K/L frames.
In the red dot world, you might like the Primary Arms ACSS reticles that consist of a chevron in the center, and a selectable large outer ring that you only see if you're not aligned on target properly. I've got the open emitter 507C ACSS in red and green, and the enclosed emitter 509 ACSS that only comes in red. I quite like the reticle, I just wish that they came in more optics options. The 509 ACSS probably isn't an option because it uses a unique mounting footprint (different from the 509T) that limits support.