I bought a 4" GP100 last October and 1700 rounds later it has been the gun I carry the most. That's because most of the time that I carry a gun, I'm going into the National Forest a mile from my house.
I love it. Wadcutters and standard pressure .38 loads are little more recoil than a .22. Rhino roller 158 grain Magnums are manageable with the right grips. Shooting a 4" .357 revolver has re-ignited my passion for the gun. After putting in serious time with a DA revolver, I'm shooting everything else better.
Having said that, I would eschew the 7 round version. Speedloaders are not widely available, and there have been reports of some types of ammunition not fitting in the cylinder.
To answer the original question, I carry the GP100 in a either a Bianchi Cyclone or Simply Rugged Sourdough Pancake.
My other revolver is a Smith 638 that I carry in either a Desantis Nemesis or Desantis AIWB holster.
I'm evaluating the idea of an "in between" revolver, which might be a 640 Pro, an SP101 3", or an SP101 Wiley Clapp.