I've got a genz benz gbe 250c 1x12 combo. It's 250 watts with the just internal speaker, 330 watts if i add an 8 ohm extension cab (165 watts for internal speaker, 165 for the extension). What extension speaker would be best for me, a 2x10, or a 1x15? I use a 4 string, dropped D, and a 5 string bass... both with passive humbuckers. Trying to compete with a guitarist with a half stack... the 1x12 just doesn't push enough air by itself. Thanks for your input..