I'm pretty sure I'm gonna go with the GK 400RB 2x10 combo and pair it up with another cabinet. My question is, would paring the 280 watt head with the 150 watt internal speakers and an additional 400 watt 4x10 cabinet be inefficient for the 4x10 since it will not recieve near as much power as it is rated for? I've heard speakers sound better when they are driven hard. Should I go for an extension cabinet with less rated power? Say 200 or 300 watts??? One other thing- The 400RB by itself is 150 watts to its internal speakers. Using it without an extension, would I really notice any difference in volume from my current 125 watt backline 115?