[quote name='spongebob' timestamp='1424083236' post='2692276']
I'm guessing I could always plug in my Markbass extension cab if more volume was required?
[/quote]
Definitely for your bigger gigs. I believe the 500 bizarrely operates at 350watts at 8 Ohms, so you need an extension cab to get all the juice out of it.
As an aside, I love the Rumble amps. I bought one of the previous gen 15's after two similarly priced Ampegs crapped out on me, and then upgraded to the new Rumble 40 (lighter, XLR out, 3 preamp voices, 4-band EQ, and built in overdrive) which I see no need to upgrade. It's a cracking amp.