Regarding 442 vs. 642, I don't think you'll go wrong with either so long as you realize the 442 will require a little more in the way of preventive maintenance. I prefer the 642 for the stainless steel's lower maintenance needs. It's a carry gun so I don't really care about the alloy frame finish as it doesn't affect the gun's function.

I've had 2 642-1s. The first finish started flaking badly within a few months of carry and practice. I've had the second one almost a year-and-a-half now, and it's only just recently started showing signs of finish wear on the backstrap (I'm not counting holster wear). So it may be a toss up as to whether you get a bad finish or not on the 642.