200 watts of Marshall tube power (I belive it was called the Marshall Major) makes my ears quiver with fear. My 60 watt 5150 cab be quite punnishing to the ears with the volume only at 11 o'clock. I'm gonna be a little honest here though. My Marshall 4x12 cab with a head is easier for one person to move around than my 5150 combo. It is a very large combo, and weighs around 90+ pounds. It wouldn't be a problem with a set of casters installed though.

Most combo amps will have an external speaker out for plugging up and extra cabinet. I think a 2x12 closed back, and 2x12 open back would sound great together. I'd get a 2x12 cab from Avatar with an Eminence Governor and Wizard combo. This combo of speakers is modeled after the Celestion Vintage 30 and G12H30. I use this combo in my 4x12, and it sounds great!

But, in all honesty, a 4x12 will be too much 98% of the time. I played an outdoor gig a while back with my Peavey classic 50, along with a drummer, bass player, second guitarist, and singer, and had no problems being heard whatsoever. Also, I wasn't being mic'd either.

I went to a bar not too long ago where the guitarist was playing through a half stack. This was a fairly small bar. If you could have taken an overhead picture of the bar is would have looked funney. There was no one standing in the path of his cabinet. It looked like a 6' wide path cleared from his amp to the back of the bar. It wasn't necessarily that he was playing too loud, it was because 4x12's are very directional. So, standing off to the side of one a bit might sound great, but move over infront of it, and you will hear nothing but what's comming out of the cab. Just something else to keep in mind.

2x12 open back cab's are the best for bar type gigs, as the open back cab produces a more 3 dimentional tone that spreads out more than a closed back. So, it is more listener friendly.