The only con to the 64 is that you can get the 65 and have the 357 option. If all you're shooting is 38, though, thats irrelevant. You'd have a tough time wearing out any of the K-frames with 38 or 38+p loads---but a CONSTANT diet of heavy magnum loads will take a toll on the K's (but this is typically over-exaggerated), and therefore some people shy away from the much easier carrying k-frames for the heavier L-frames, which were better designed for CONSTANT magnum use. IMO, few people ever run enough mag loads thru anything to make much differance.
I have 4 mod. 66's right now, and think its one of the best revolvers, if not the best, ever built.
I recently sold off my rare 3 inch barrel version, because some guy was willing to pay any price, but i'm sorry I did now.
Had a 617, 6" once--to much gun (weight) for a 22, unless you only shoot off the bench