Bill Fitzmaurice

That was done to save amps from being cooked by impedance loads that players employed because they didn't know better. I will confess to having done that, running 2 ohm loads with Fender amps that wanted no less than 4 ohms. But that was the '60s, we did all sorts of weird things then and managed to survive, and those Fenders were built like a Centurion tank.

Not really. The only time it might is if your amp is so underpowered that it can't drive the 8 ohm speaker to it's full displacement, which would be rare, like with a 25 watt amp and a 200 watt speaker. A 4 ohm 15 makes some sense if it's paired with a 410, or even a 210, to get the sensitivity of the 15 high enough to match well with the 210/410. But then you'd need a 2 ohm capable amp, not to mention the inherent flaws of mixing speakers. Oops! I did mention it. 😲

It's not about watts, it's about voltage sensitivity. That's 3dB higher with 4 ohms, so with the same amp settings the 4 ohm speaker will be 3dB louder, assuming all the other T/S specs are the same, which they seldom are. 3dB is audible, but just. As for maximum SPL that's mainly determined by the cone displacement, T/S spec Vd. If Vd is the same maximum output will be the same, again if all the other specs are the same, which they seldom are. The 3dB increase in voltage sensitivity comes at the cost of drawing twice the current, which some amps don't deal with very well.

If that's with guitar amps the speakers are contributing to that clipping, by virtue of the short xmax and break up modes of guitar drivers.

https://www.midbass.com/how-to-understand-ts-parameters/

Upgrading is possible, if you have a basis for comparison. At a minimum that requires testing your speakers for frequency response, and knowing their T/S specs.

At least we're not using cubits, though they did manage to build the pyramids with them.

In the US metric hardware, as in nuts and bolts, have pretty much replaced Imperial entirely. It started with cars, when the best selling cars in the US were all Japanese, and the US manufacturers were forced to follow suit. It became complete when almost every product made was of Chinese origin. But as for going full metric about the only product that has done so is alcohol.

So when I watch British TV programs (which is almost every day) why do they keep referring to feet, pounds and miles per hour? 🤔 It reminds me of the story of the man who was confused while visiting Quebec. The faucets in his bathroom were both marked C. When he asked the front desk why they both said 'C' the clerk replied 'the one C stands for Cold. The other stands for Chaud. We are bi-lingual.'

Burying a post at the end of an unrelated zombie thread tends to be unproductive. You should start a new thread.

Pretty much any two cabs together will sound better than either alone. The only way to know if Cab A plus Cab B is better than 2xCab A or 2xCab B is to try all three combinations side by side. That's not an option for most.

Cheap connectors are the likely problem. Are your cables equipped with Neutrik? If not replace them- the connectors, that is, not the cables.

It only delivers 180w into 8 ohms, so you won't have a lot of headroom. The i Pro 600 V2 is a better match.

Everywhere. It can't damage anything, and will displace any residual moisture

True, so I'd spray the inside with contact cleaner, including in the pots.