Robert,
The slip-on grips will typically make your grip larger in the hand. If that's not an issue for you personally then I'd suggest picking up a Hogue over-grip and be done with it. If that's not an option for you, then definitely knock down that Gen 4 texture just a touch. It won't take very much as those have the box-style stippling rather than the dot-style stippling that's on the RTF Gen 3's.
I have a G17 in RTF Gen 3 and I absolutely know how you feel. Against bare skin it's like rough grit sandpaper directly on the body. Against clothing it just roughs up the material, it can ruin Under Armor type shirts rather quickly.
One of my students suggested a decal grip some time ago to give it more of the feel of felt, but the tackiness of the RTF grip type. I checked his out and if I didn't have issues with it increasing the grip size I'd be willing to give that a shot.