Power in RMS means little, other than the obvious difference between 750W and 125W...
The only significant stat is SPL at a specific THD. In other words, how LOUD is it, before distortion gets up to an audible point?
And this is the ONE stat, in a sea of meaningless specs, that you will rarely EVER see anyone publishing. But they will print page after page of other bullsh*t for you to argue over endlessly. Anything other than the ONE stat that would put the questions to rest...
One thing I haven't noticed on my friend's L1 system is any kind of clipping or limiter engagement light. Me, I kind of like to keep these things from flashing, but if a system doesn't have one, it's tough to tell when you are bumping into the system ceiling unless you grossly exceed it. They certainly help in making a store comparison. What clips first, at what volume, and how well does it deal with it? That's a real world necessity, IMO...
One thing I like to take to stores when checking a PA is a board tape (or, rather, CD). In other words, record your act exactly as it is going to hit the speakers. If you listen to a commercial CD, they have been compressed and limited VERY professionally, and modern CD's have very little dynamic range, so a PA can sound quite good even at pretty high SPL's. But a board tape has none of that dynamic range reduction... If it is a live band, the drum transients are still there, the peaks and jumps in your own playing and singing are still there, you will hear what the audience hears through that PA as if you were playing.
You may find it to be a LOT lower in volume when you start to hear a bit of distortion creep in.
BTW, if you find yourself in this kind of position, I cannot recommend too highly a little inexpensive compressor by FMR Audio, the RNC1173. It is specifically designed as a stereo only, three stage mix compressor (in other words, rather than the mix being compressed once to get the level reduction you need, it uses three stages to reduce it, each being gentler and more transparent that the one needed to get the same gain reduction). Under $200 last time I checked, and capable of making a band sound EXACTLY the same, out front (you don't WANT to squash your sound if it is a good one!), but magically take a considerable 6-10db or more off of the peaks, and let your PA run without clipping.
It is a magic box...