Sour d, have you tried anything higher in wattage than that 15 watt blue? Curious because I just bought an extension cab for my small amp rig (tweed champ and 80's sidekick 15 watt) and am trying to max out headroom on the champ. I know the blues are some of the best speakers for this amp, but I am really wanting to put something > 15 watts in it if it will sound pleasing. Curious to hear successful champ, or 5 watt amp, and 12 inch speaker combos.
I tend to like my speakers to be able to handle much more wattage than my amp puts out. I'm not big on speaker distortion. Rather than just thinking about small amps, consider ratio. Trey used his 22w Deluxe Reverb (a small amp by some standards) with at least a 4x12 of Celestions Blue's totaling 60w power handling. Some people use 1 Celestion Blue for a Deluxe, so he has 2-3 times the power handling necessary, plus I believe he at least sometimes kept the combo's internal speaker plugged in. At some point in time, he was using a 50w Weber Blue Dog; if he used this with the 412, it would total 110w power handling for a 22w amp.
Similarly, he uses at least a 212 with V30's for his Mesa Boogie Mark III. The 2x12 would handle 120 watts. His Mark III is Simulclass in Class-A mode, which usually puts out 15w with EL34's, but he uses 6L6's, so his Mesa would probably max at 30w in that mode. Not to mention his master volume is on 3 out of 10. So again, he is using at least 4 times the power handling than required by his amp. Not to mention if he uses both 212s, then he has over 8 times the power handling indicated by the amps max output based upon his settings.
The Mesa originally came with a 200w EVM12L speaker, which is about 3x the power handling of the amp in Simul-Class mode. Likewise, I think many amps come stock with speakers that would be unlikely to get fried by the amp. Fender sold various versions of the 15w Blues Junior including ones with a 50w handling C-Rex or 60w handling V30.
Conversely, there are many people out there with the opinion that you have to push a speaker near its limit to get it to give up the goods. That is not my opinion. I could see that for some heavier classic rock tones, like the ones made popular by a cranked 100w Marshal Plexi going into a 412 cabinet with Greenbacks that handle 25w each. Then you have a 1-1 ratio of power output and power handling. However, this is not the sound I go for most of the time, and not a sound I think is ideal if your aiming for a jammy tone a la Trey.
However, other aspects of sound will be influenced by increasing power handling. For example, going from a Blue to a Gold will be warmer top-end and less bouncy with a punchier bass. Of course you could go from a 1x12 with a Blue to a 2x12 or 4x12. You'd get a bit more warmth in the bass without too much effect on the top-end of the speaker (retain more chime than switching to the Gold possibly). You might retain a bit more of the bouncy feel that goes along with lower-wattage power handling speakers. And the speaker(s) would be less likely to distort as the amp's volume increases.
So the difference is probably largely preference. I went with a 212 with V30's because nothing else sounds the same and they are affordable. 212's sound a bit better than 1x12s, but are less portable. I don't think a Blue that handles 15w will distort in a 5w champ. A Gold might sound bigger and warmer, but somewhat less bouncy/lively. A 212 with Blues might sound a bit bigger while retaining the bouncy feel, but I don't think it would be cleaner or louder (since even a single 15w Blue would not be pushed near its max) - it would largely be due to the bigger cabinet.
