Amp's nominal power rating - any use?

Isolated output power ratings hardly tell the whole story. You could buy a receiver rated at say 150 watts/channel and know it could`nt keep up with a Pass XA.5 30 Watt/channel at all. That Frankenstein is an 8 watt beast due primarily to excellent custom transformers and an enormous power supply, it uses the 6EM7 tube as a driver for the 300b(supplies a lot of current). A case of quaility over quanity.

Meant Pass XA30.5

Its probably the best reasonable rating anybody could come up with without getting to much into specs that are hard for a lot of people to understand.If they give it at full bandwidth,it sure helps.The speaker being driven creates a hard power rating spec for a one fits all amps.Their impedance,(speakers resistance) is always varying making power ratings tough for amps rating.Amp matching with speakers can be more critical than watts.Speaker efficiency is very important also.Doing some research on whether your amp will drive xyz speakers can be more useful,especially if they have low impedance dips.

I have no idea what Kijanki is talking about, with his percentages.

Your speakers are good for about 87db for 1 watt into 8 ohms (at one meter). This means an amp that clips at 8 watts will drive the speaker to 96db at one meter, which most people will consider quite loud. I would suspect a lot of people don't really listen to speakers this small any louder than that.

The 30 watt amp will be able to drive the speakers 6db louder, all things being equal, and they probably aren't. 6db is pretty significant, but since the 6db is 6db over 96db, you may not notice it, depending on the music you're playing, the size of your room, and your average listening level.

Since these are single-ended amps you're talking about, they will have a sonic signature, and the transfer function differences between the amps just may overwhelm the power differences.

Have you ever connected your speakers (which are pretty good for speakers of that size) to a decent solid state amp of, say, 100w/ch, just for grins?

High-end amps almost always achieve their claimed wattage ratings, but there are amps and then there are amps, and in this regard, what Charles1Dad wrote is true: an amp with massive power supplies (and if it's a tube amp, one that also has the highest quality output transformers) will sound considerably more powerful than most amps of the same wattage rating. Very few amps fit this profile, however (and the ones that do are very expensive), so you're basically stuck with wattage ratings.