Karl,
It gets to the point, where at some exact specific place at some shows , every mic will clip. If its only happened to you a couple of times (meaning far fewer than more) it may just be that those few instances, at those shows were just too much. If it is happening a lot, you may want to get those mics checked out. Seeing as how you're running them 3w, they should be fine the vast majority of the time.
(Maybe your BB is f'ed up also)
I taped Ministry last summer..ran U853>8532s, those are the AT power modules. They raise the SPL handling on my mics to around 144db before they will tweak. Now, I can tell you, and Andy (junk) can verify the absolutely fucking insane volume that they were playing ..I was able to tell just by how I had to set my levels that these did/do in fact, handle (quite a bit) higher spls than my ps2 (haven't clipped this yet)setup. I had my HI-MD levels completely maxed out and was *barely* hitting midpoint on my levels. Still, when I got home and played it back, there was a very faint hint of clipping. I'm pretty certain, with the volume that show was, it would be very difficult to pull one that wouldn't.
Point was, that show was just a little past that point where my mics could handle it.
If Andy hadn't had an extra set of earplugs, I can safely say I would have walked out...it was that loud.