Glock, XD, S&W, they're all the same, point down range, pull trigger and BANG.  All are quality makers with S&W probably having the better CS after the sale.  I've owned several small S&W auto's and liked them all.  Currently, I shoot a XD Tactical.  The new XDM has a match grade barrel, but I doubt any of the shelf S&W auto's have such a barrel.  Now you could save and save for a Performance Center S&W 952 which is a top of the line shooter.  I have one and you cannot compare it to a stock everyday handgun.  Why are you trading away your current XD for a new XDM?  As far as S&W backstraps, just the M&P can be changed, not the other models.