I'm used to AMD motherboards.
You didn't pick an AMD motherboard...so what are you saying?
Anyway, the main feature that the X48 platform offers (the one you suggested) over the much cheaper one (P45) is the ability to use Crossfire. Aside from a few less important differences, it simply costs a lot more. If he were getting an ATI card it might make more sense.
On the other hand, the X58 platform is a major upgrade from your standard Core 2 setup. Triple channel memory, an integrated memory controller and native Crossfire
and SLI support make it a worthwhile investment. I7's have plenty of room for overclocking and support hyperthreading as well.