this plus a couple hundered more for water cooling and you're set
add an extra 100 for a good set of ram... and the item that got cut off on top was a asus dvd optical drive
Anyway, if I'm seeing this correctly, AUD is actually more valuable than USD, so $4000 is one hell of a budget for a gaming PC. Not only will something of that caliber be able to max current games, it will probably be able to max them out at 60+ FPS for a good 5 years if built with some thought.
Anyway, grab two 590s or two 6990s for Quad-SLI/ Quadfire for about $1500. Games can't use six cores, so 980x is a silly investment. 2600k showed a little performance boost over the 2500k in recent benches of The Witcher 2, so I'd say grab the 2600k if the budget is as-is; otherwise 2500k is fine for the build.
Grab a nice z68 mobo, 12GB of RAM is more than enough, throw in a hefty SSD and a nice HDD, a nice 1200-1500W PSU, and you're up to a good 2500 bucks.
Grab a Corsair Obsidian 800D, throw in water cooling supplies and a bunch of AP-15s and you're still not up to $4000. Seriously, he can buy whatever he wants with the exception of stuff like this.
He can buy the best pieces of hardware, and ask the water cooling people for suggestions on water cooling stuff. This is going to be one hell of a PC, tell him to keep OCN updated with a worklog.
And best of luck to him! Going to be a fun project for sure.