My 640 (no dash) was produced around 1990 before S&W stretched the frame for the 357 mag. I do believe that they made a 38 sp. chambered 640-1, which had the longer frame, but that's not the model I have.

I found the thread about the +P+ loads interesting.
I currently use Buffalo Bore's take on the FBI load which they claim 1040 fps out of a 2 inch Mod 60.