That Mesa cabinet is absolutely ideal for the B1500. Unless it's been modified somehow, it's 99% a 4 ohm cabinet...there were a few upgrade options for that cabinet, which would affect the overall power handling. Here's a thread on it:
http://www.talkbass.com/forum/showthread.php?t=267162
http://www.talkbass.com/forum/showthread.php?t=267162

I picked up two Carvin BRX 10.2 Neo cabs from a fellow TBer for a really reasonable price. While they weren't number one on my list, they were the very first cab set I was considering - and for the price, I don't think they can be beat.
