I have a M65-5 (3" round butt) which is my "nightstand gun". I use the Federal 158gr SWHP +P loads. K-frames can handle .357 magnums, so 38 +Ps won't be a problem. The only advantage to the M66 is, of course, the adj sight. It is true that adj sights get caught up in stuff easier, and they can get bumped out of alignment. But, I think the adj sights on my M19 (red ramp/white outline) are much easier pick up on target. The M64 and M65's are just a matte stainless on matte stainless sight picture. Round butts are easier to carry concealed, square butts are more of a target grip. Either way, a K-frame loaded with a quality 38 round is a great choice for home defense. You may want to look into the Winchester PDX-1 38 special load. I have tested the same round in 40 S&W and they appear to be, well, lethal to say the least.