I have approx 800 rds through my 4.5" model. Very reliable and I fired over 500 before doing any real maintenance. (just snake the barrel.)
I don't like the 4.5" barrel. The 5.25" w adj sights n fiber optic front is the way
to go. Colt Govt is 5" and IMHO 5" is just right. Cost fortune to upgrade my XDMs sights to 5.25s configuration. Adj sights won't even be milled into slide.
Range: how you grip the pistol can change POI more than you would suspect. Higher lines -wee bit more flip. Took me some time to warm up to it.
Custom shop can shrink groups by half. I talked to some of their CS staff.