Difference between New and Old Amp WPC ratings....

Yes there is a difference with power ratings with old amps and new, if of course you are talking 70's amps or even reciever. From wikipedia, In the US on May 3, 1974, the Amplifier Rule CFR 16 Part 432 (39 FR 15387) [3] was instated by the Federal Trade Commission (FTC) requiring audio power and distortion ratings for home entertainment equipment to be measured in a defined manner with power stated in RMS terms. This rule was amended in 1998 to cover self-powered speakers such as are commonly used with personal computers.

Before this rule less = more by todays standards.

I have a Pioneer SX 626 rated at 27 wpc, by today's standards it's like 3 or 4 times that

Actually, I believe (not 100% sure) that there was another rule change subsequent to 1998. It actually had the effect of going the other way as IIRC it reduced the preconditioning stress and discoutaged and/or disallowed the power RMS @ X% THD over bandwidth spec that had been traditional. Someone with more energy might want to research it further, but the current specification regime is I believe less useful than previous.

Apologies in advance if I screwed this one up, but I'm pretty sure there's a kernel of truth in here smoewhere.

Marty

Not all wpc are created equally. Some amps, not necessarily new, sound significantly more powerful than others of the same power rating. I have heard the class A Bedini 25X25 sounds huge for a 25wpc amp. The classic NAD 3020 kicked out an amazing 20wpc. And tube amps can pull off the same trick.
Me thinks there is much more to the equation than the wpc rating, whether using the old or new standard.