I played my Alembic Series I and WXT500 tonight at the Ogden Theater in Denver and had three guests play through it as well. The other bass rig was an SWR, which was OK, but the consensus was that the WXT500 sounded clearer and deeper. The stage sound was big and full (core 4 piece band with 4 piece horn section and various singers/guitarists/fiddlers/banjo, etc. We were covering the Band's Last Waltz to a packed house) and it felt great in the house. I've beat the crap out of it on a regular basis, with output limit light lighting up with each note (although not continuously on) and it just keeps going. Not quite as satisfying as the WP100/Crown XTi4000 rig, but almost and it certainly has been a great backup. The two have a different tone stack, but the sound people who I work with regularly don't seem to notice too much of a difference. If anything happened to it, I'd get a replacement.
My experience with MarkBass stuff is much more limited, but I didn't really get along with the tone. I bought one of their lightweight heads a while back and returned it the next day. I know some people love them, but it wasn't for me.