Every receiver is different, but in general:
HK underrates their receivers
Marantz and Denon usually hit their stated specs
Onkyo usually comes close to their states specs
Sony, Pioneer, and Yamaha overrate their receivers
The 918 was measured at about 37 wpc into 5 channels. See the following which includes measurements:
http://www.hometheatermag.com/receivers/808piorec/
That said, 37 wpc is likely enough if your speakers aren't particular hard to drive.