I'd agree at a general level with this, if we're talking about class D solid state amplifiers. They can go into nasty square wave clipping at somewhere as low as 59% output. Also, a tube amp can output, at certain transients, double its rated power. Class D amps don't do that. These general statements don't apply to modern class A/B and class H digital amplifiers though. Companies like Matrix and ISP don't use class D; and their power amps behave differently. The sine wave clipping characteristics can become desirable, similar to tube amps. Also, because it's been mentioned in this thread; headroom applies to the max dB level your speakers can produce within their wattage rating vs the dB level they're currently being pushed. For example: a V30 can produce 121dB at 128w. If you are sending 32w to it, the speaker will produce 115dB, leaving you 6dB of headroom. You are utilizing 25% of your 128w available. Power amp wattage rating vs cab wattage rating does not indicate headroom. It's clearly an integral part of pairing the two devices, but not the determining factor. Ultimately, the feel in the room and your ears are still the deciding factor in what sounds best. All the specs and data sheets in the world mean very little when you put my Mesa 2:90 up against my ISP Stealth or my other guitarists' Matrix GT1000FX. The digital amps are fantastic for their sound characteristics and weight advantages, but I'd think anyone would still take the 2:90 tone and feel in the room over the other two. The mass majority of places we play live have a full PA and sound guy, so I typically use the ISP for stage volume through a 412, and go FOH with the main output, which works perfectly and sounds awesome. But if there is no PA, I'm lugging the 2:90 every time; along with the ISP, as it is so light, it's the perfect backup in those situations.