Receiver power
Both those receivers should have plenty of power for 8 ohm speakers in a medium sized room. However, based on the AH review, Yamaha is conservative on the power rating of the RX-V659.
Also note, if you double the power (50 watts to 100 watts) you only get a 3dB increase in volume.
I have the HTR-5860 (last years model) and would recommend it.