I just bought an old GK 400 RB head on Ebay. I was wondering what kind of speaker cab people have had success pairing this with. Also, how much volume can I expect to get out of this head? How would you describe the sound? How many watts should I look for in a speaker cab to compliment this amp? Should I go with a 15" or 12"? I seem to like 15" speakers for their warmth and punch for both electric and upright.