I just changed from a 5820K and Gigabyte X99 to a gigabyte 570 elite and a Ryzen 5 3600 and with the game I play it made a noticeable difference. The game is smoother and I can jump further than before.
I find it hard to believe that you have had no issues with the X99 platform, they are notorious for usb problems and form time to time other issues. It was fast @4.5 gigs but this 3000 seems just as fast and smoother.
I can bet you will see a noticeable difference going with the 3900x, however you need to upgrade your memory because these 3000 series cpu's like fast memory. Good luck