Jason, a couple of comments on some apparently misunderstood points. The FTC power regulations that all amplifiers sold in the U.S. have to comply with are interpreted to require that the rated power be measured with at least two channels driven simultaneously at that full rated power for at least five minutes continuously. Typically the rating is at 8 ohms, and five continuous minutes of full-power operation(unrealistic for home use of course)at 4 ohms couldn't be accomplished for an "official" 4 ohm rating. A single channel rating could be stated in addition, but wouldn't be acceptable for the basic power rating. Some manufacturers choose to instead use an all-channels driven rating instead, but this doesn't appear to be of much relevance to real-world use for home audio, as has been pointed out frequently. For example, Audioholics in their lab tests use one and two channel measurements as being more realistic. Tests, such as those on the 3808 that Michael linked, show that the advertised power ratings are met in reality, as would be expected, since manufacturers would be foolish to violate what is essentially the only set of legal restrictions that exist in the entire realm of audio equipment.
Also, there's no meaningful factor of faster response or quicker attack which differentiates amplifiers. If an amplifier, regardless of whether it happens to be in a receiver or not, can amplify to at least 20KHz with flat response and low distortion(as is common these days in even modest-cost units), then by definition it has to have an adequate slew-rate and the related rise time for human ears. There's no magic in separate components which may or may not have slightly better measurements which have no audible effect.
