Conrad Johnson Premier 12, how powerful?

I've read in several places that the CJ Premier 12 is not great for inefficient speakers. This is surprising given that they're rated 140 wpc. How inefficient is inefficient? I have Opera Callas monitors, which are 87 db. Is this inefficient? I'm trying to find a tube amp, but power is very important. I don't like merely 'adequate' power.