I'm almost certain the Pioneer Elite VSX52 is a twin of the 1015. The Elite 52 rates out at 110x2, 20-20,000, 8 ohms, at .09 THD. Interestingly enough, the Elite 54 contains the exact same specs as the Elite 52 and 1015, but weighs in at over 39lbs. The monster Elite 56 again, same specs, but jumps in weight to 44lbs.
http://www.pioneerelectronics.com/pna/product/detail/0,,2076_4155_123728223_tab=B,00.html?compName=PNA_ProductDetailComponent
If you look at pg. 75 in the 1015 manual, it's the exact same rating listed under "total harmonic distortion."
The figure of .09 is closer to Yamaha's RXV series ratings of .05. Power output will continue to climb, but THD also climbs fairly quickly at the poles of the Hz range. This is why sometimes you'll see the 1kHz rating instead of full bandwidth of 20-20,000Hz. Pioneer, if they wanted to, could state a 150x2, 1kHz, 6 ohms, at 1% THD.
The Yamaha 5890 can state 140x2, 1kHz, 8 ohms, at .7% THD. The 5990 has no such specs in the manual. Basically, the Yamaha has a slight edge over the 1015 - but probably not audible. It's nice to see they've stuck to an 8ohm rating and lower THD at 1kHz. The 5890 specs are 120x2, 20-20kHz, 8 ohms, and .04 THD (identical to the 5990).
What you'll find that varies more than wattage figures are features and the mass of the unit. It's odd to see all the Pioneer units list the same power output, but vary in weight up to 10lbs. You'll see this in HK AVR's. Big weight, but conservative output ratings. The more weight, the larger the power supply, the larger the heat sink, in turn the cooler the unit runs, and the longer the unit will last if pushed to its limits.
Don't beat yourself up. Find a great deal on one of the units listed in this thread, and enjoy the music.