peak X .707 = RMS right ? just as long as they tell you if it's peak or RMS it doesn't matter which rating they use

Nope. If that's some kind of "standard" formula, I don't think any companies are following it. None of the peak-to-RMS ratios I've seen match it.

More often, the Peak number is a meaningless arbitrary number somewhere above double the RMS rating. The less reputable the company, the more spurious the number. Once, a long time ago, I bought a pair of really cheap speakers that were advertised as "200 watts". That was a peak number. No RMS rating was given. In reality, the speakers could probably handle about 5 watts (they were really cheesy).

Another trick I've seen is when a company reports the peak wattage at a 2-ohm load. I saw an amp in Crutchfield with a big "750w" painted on it. The "750" was based on peak at 2 ohms, but it was actually a 150x2 RMS amp at 4 ohms.

The RMS number is the only one you should pay attention to. And since companies seem to differ in how they report the Peak number, you can't determine an accurate RMS number from it.

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Tony Fabris