I had a proclip mount in my WRX. It was nice and all, but would move around sometimes when I tried to take the phone out.
When I sold that car and got another vehicle, I used just the proclip phone holder and made my own vehicle mount. Made a metal bracket that bolts into the radio hold down screws and comes out from behind the radio bezel. Bolted the phone holder to it and it sits exactly where I want it.
My advice for a MotoX with a very thin case: I previously had an HTC Rezound that I used without a case. The Rezound was much thicker than the X, but the exact same height and width, so the X fit in the holder width wise, but was a little loose front to back. I took the holder and held it over a candle at the corners and slightly bent each side outward when the plastic got soft. Now with a thin case on the X, it fits perfect in the mount and holds it very securely. When I want to take the case off, it still fits and sits vertical in the mount, but rattles around slightly.