My son just built a system "with his money". That is a strange concept since I'm paying for his college!
"high end gaming" is extremely open ended and ever changing. You can get cards from next to nothing to several thousand and you may or may not see any benefit. It looks like the board has onboard graphics and those have been greatly beefed up recently. Also, the CPU/MOBO graphics are now being used to assist add-in cards.
I know people that have spent the thousands and replaced the cards within a year because they didn't perform as well a lower end card on their game.
I would suggest you build the system without a video card, but plan in the ability to add a good one. Test the onboard video with the program(s) he wants to run and do some testing. This establishes a baseline and may be perfectly acceptable. Then you can add a video card immediately, if necessary. If not, you save the money now and have a relatively inexpensive upgrade path down the road.