This is just some great classic rock tone and playing by Clapton using two 1959 Superlead 100 watt Plexis and a of course the Gibson es-335. Clapton has gone through many different rigs and setups over the years but his sound with Cream captured here is definitely a classic signature rock sound.
Today two Marshall full stacks may a bit on the impractical side for most players but at the time of this video sound reinforcement for big venues was definitely in it's infancy. As bands like The Who and Hendrix started to raise the decibel barrier and rock and roll started playing to bigger venues, it made perfect sense as the P.A pretty much only handled the vocals.