Sounds like something we can do. Have both. (2” .38 Rossi and 4” .38 Rossi). I was thinking about getting one of those grip laser’s for the wife’s carry (pictured one like it above).
The thing about the laser, however, is much faster target acquisition in high stress situations. You aren’t dealing with much distance when talking about home or personal defense situation, 15 yards max with the probability of it being much closer so I think except for range play, the increased accuracy of the 4” is moot.
If you’re gonna do it, please make sure you include the 2” results with the laser turned off. Lasers can have batteries go dead, whereas 4” barrels never lose their sight.