Regardless of whether you have $5000 to burn, spending it all in one shot on a PC is ludicrous. Technology gets outdated too fast for that purchase to make sense. For $3000-3500 you could have a VERY good system, and have money left to upgrade down the road to keep your rig "with the times." Hell, you could buy an E6400/E6600 now and a quad core in a year or two....and still spend less than what a QX6700 costs now.
Although many of us including you may disagree with spending so much money on computer hardware, I would just let him do what he wants. If he wants to spend his $5000, the let him. I'm sure he will enjoy it plenty You can't flame him about some informational help. Hey, i probably spent over $2000 on my last build in the summer