Need 4gb... dual channel? 2 stix? 4 stix? 3 stix?

My brothers wants to throw 5k at a crazy insane system... but just because we have a huge budget dosen't mean we don't want to cut costs where ever possible...

He wants 4gb in his system... I'm thinkin 2 2gb dual channel, cheapest well known brand is gskill 2 2gb dual channel kit for 279.99.

But will he see THAT much more performance out of dual channel? Or would it be more worth it to get 4 1gb stix or 2 756 and 1 2gig?

I certainly have had better luck overclocking with 2 modules versus 4.