Congrats on your Rumble 200! If you'd posted this in the Rumble Club you'd likely get more answers as well. One thing I'd point out is that combo is 200 watts at 4 ohms with a second cabinet, 140 watts by itself. That said, 100 watts into each cab is not a lot of juice for some cabinets, but I think you'd get a big bang out of another Rumble 1x15 ext. cab and others could explain the physics behind having two same size speakers. I would add that GK has some very nice powered cabinets like the 115MBP that would give you an extra 200 watts and an extra 15. They also have a 112 and a 2x12 in that line, but I don't think have at 2x10. I LOVE my Rumble 500 combo with an add-on 2x10 cab for four ten inch speakers and it is plenty loud. If you don't need the power, maybe just add a Rumble 1x15, that would be some nice tone! Good luck and let us know what you decide.