I've owned 3 M65's, and still own 2. My first one was customized by Karl Sokol of Chestnut Mountain Sports. I have a 3" and 4" stock now.
My personal opinion is that the M65 is quicker and more natural to shoot than the M66, just due to the sight configuration. Much better for CCW, too, since the sights don't snag on clothing or dig into your skin.
I'm not trying to start anything against adjustable sights, but I've used the fixed sights more, and I've had adjustable rear sights loosen up on me. But, I still own many S&W revolvers with adjustables, too.
The $350 price is high for a 4" gun, but not completely outrageous for a 3", from what I've seen anyway. The only available 3" M65 available now is a Ladysmith.