I'd agree with not going any lighter than needed 100%. The OP is interested in fishing for bass, so that's certainly on target. Having said that, I need to drag out this picture from April 7, 2009 (sorry Ard
I was fishing for stocked trout using a 9'5wt Z-Axis, a 9' 4X leader, and a #10Wooly Bugger. That bass made several runs (I'm much more of a smallmouth guy, but this LMB wasn't rolling over easily). It's the largest LMB I've ever caught, and not what I was expecting that day.
Two Big Mouths (you can see the small Wooly Bugger in the bass's mouth):
I should say that I've lost a considerable amount of weight since that day.
Also, if you're fishing a light leader, and hook a monster, stay calm and get the job done. It's definitely possible, but I would have used a heavier leader if I were targeting bass that day.
P.S. Don't even ask why I'm holding that little trout net. The bass wouldn't fit, but I was too excited to put it back on my vest.