Well I just played with the 6390RDS. Absolutely the best Safariland holster I've ever owned and I've owned many. Perfectly fits my G19X with threaded barrel and Leupold DPP and tall sights without any mods (except the barrel plug but thats a 30 sec fix). Did the usual stuff like installing the QLS fork plate.
Rock solid, no play with the X300 light and draw is just as quick as my Trex Ragnarok holster.