The Intel core i7 2600k is overkill for gamers as the Hyperthreading isn't needed as most games don't use more than 2 cores. If he is video editing, however, then the 2600k would be helpful. 2600k = Waste of $70-$100
EDIT: Overkill on PSU? A 650W would be more than sufficient
In gaming, no, the 2600K is not better. Unless you have something like 3 580s or 2 590s, you will not be bottlenecked by a 2500K. The GPUs will be working all out, but the 2500K will have cycles to spare, so getting a 2600K, which will have *more* cycles to spare, will give no performance increase.
A 650W PSU would be fine for one 580, and an 850W for two, if they're good-quality units (http://www.newegg.com/Product/Product.aspx?Item=N82E168...).
On your average system the card requires you to have a 650 Watt power supply unit.
GeForce GTX 580 in SLI
A second card requires you to add another 250 Watts. You need a 900+ Watt power supply unit if you use it in a high-end system (1 KiloWatt recommended if you plan on any overclocking).
For each other card (3-way SLI) that you add, just add another 250 Watts and 20A on the 12V rails as a safety margin. What would happen if your PSU can't cope with the load?:
bad 3D performance
spontaneous reset or imminent shutdown of the PC
freezing during gameplay
PSU overload can cause it to break down