I'd use 3 gallons for extract brewing. With that, you won't get boil over with your current pot...and it'll be easier to cool your wort with cold top off water.
On Tap: Barleywine, Coffee Oatmeal Imperial Stout (big big beer)
Fermenting: Double Simcoe IPA
On the Bench: Racer 5 IPA
"One of the first things early caveman did, when he crawled out of the mudd, was to make beer. And cavemen everywhere are still making beer...and drinking beer." - Jean Sheperd