A lot of PA cabs are designed to cross over to subs.
A bass cab will often go lower than a PA cab, because it's designed not to be crossed over. If you want low end then this is a good thing.
Some of the nicer PA cabs discussed in this thread are designed to go lower and run without subs. This means you get a DSP controlled bottom end (more controlled than your bass cab) and the high mids/highs are coming out of a much nicer driver too compared to your Bass cab