If you use IEM's for big gigs, then you don't need to worry about a modular rig or lugging a big stack....All of it, except playing in stadiums. If i ever will fill a Stadium with my music, i'm sure there will be some Roadies, Groupies and a suitcase full of Dollars
2.000
Most indoors, when we play bigger (and outdoor) gigs, we play ampless with our in ear monitoring system.
Ok, but i love 15" Speakers, the Rumble 500 has 2x10.
I still strongly recommend that you try the 200 and 500 back-to-back before you decide.
You've still got those small to medium club gigs to worry about, and the possibility of playing with other drummers over the life of that 5-year factory warranty. I don't know anywhere else in ampdom where you can get so much potential loudness increase for only $100...
Also, the V3 Rumbles don't sound like the old ones, and loving 15's is less relevant these days than at any other time in history. High-powered 15's can sound "faster" and "more modern" than most 10's, and some modern 10's go deeper and are punchier than any old school 15 rig.
I say this having owned and gigged both, and IME you can't make generalizations by cone size any more. For example, I have two single 12's sitting in my living room right now. One (Rumble 100 V3) sounds like a quieter version of an old-school twin 15 stack. The other (AudioKinesis TC112) has custom drivers, can go deeper with EQ than most cabs of any configuration, and is neck and neck with a Rumble 410 for maximum volume (when driven with enough power).
WOOT! 
