AFAIK, the MPulse 360 is a scaled-down MPulse 600 - have a look on Talkbass, there's a fair bit of tonal comparison between the Walkabout and the 600 on there.
I've owned the 600 and the Walkabout. I preferred the Walkabout, as it had inherently stronger mids IME, but they're both great, great heads.
The Walkabout has its' flaws - no mute, hopelessly impractical post-everything DI, no speakons, but the main problem with it is... it's stupidly, stupidly, expensive. Like.. stupidly.
Anyway, I've ended up with the Genz Streamliner, which IME has a real Mesa Simul-statey thing going on, and it punches like the MESA heads do. A lot cheaper, and a lot lighter.
Something to think about...