I, like Continental Op, like my carry guns to have as close to the same sight picture as possible. My main carry is a 640-1. I painted the front sight bright green and blacked out the rear. I did the same with my bug, a 637-2 with a bobbed hammer spur.

Now, I'm no long distance shooter, but this works for me out to 15 yards or so with either gun. My recommendation would be the standard 640, however either makes a great carry piece!