I asked the same question a year and a half ago, except I was looking for blued, so it was GP100 vs 586. https://thefiringline.com/forums/showthread.php?t=581268
I bought the 4" GP100 and have no regrets at all. I replace the front ramp with the Ruger red ramp http://shopruger.com/Ruger-GP100-Red-Front-Sight/productinfo/90074/, but from what I understand Ruger has done away with the drop-in front sight. Also put these grips on it http://shopruger.com/Rubber-Grip-w_-Rosewood-inserts/productinfo/70083/
I bought the 4" GP100 and have no regrets at all. I replace the front ramp with the Ruger red ramp http://shopruger.com/Ruger-GP100-Red-Front-Sight/productinfo/90074/, but from what I understand Ruger has done away with the drop-in front sight. Also put these grips on it http://shopruger.com/Rubber-Grip-w_-Rosewood-inserts/productinfo/70083/