Understanding amp drive vs wattage

[Isher]

I've been looking at going to a 2 amp setup for a while. I do something similar with an SVT4 and SVP-Pro (using the 4 in stereo). I like to play around in Amplitube to sort of "pseudo-test" what I'm looking at.

I'm really leaning towards an Ampeg V4BH, but in a nice surprise, I really liked the tones I was getting with a Jet City JCA20H for dirty stuff. I had the V4B in Amplitube dimed out with about +6dB of boost just to get it to start breaking up. Then used the JCA20 sim with the Master all the way up, Gain about 3. Both were using 8x10 cabinet sims. But that's a digital environment with gain staging options galore--not a real world scenario.

Just seeking to understand from some more knowledgeable minds...I know all things equal, a 10W amplifier will be 1/2 volume of a 100W amplifier, but if I'm using two amplifiers, how would I go about trying to make sure one isn't ridiculously louder than the other--especially since they both are tube heads? I had thought about a JCA50H's 50 watts would be about on point with the V4BH, and I've read a few magazine articles that say a bass amp should be about twice the wattage of the guitar amp as a rough guide, but that's comparing guitar to bass.

Should I just go for a JCA100H so both wattages are equal? For what it's worth, I plan on using good attenuators on both since I play in smaller venues, for what it's worth. Whenever I end up in a bigger venue, there's usually a FOH set up I can use a speaker-level DI with.

[rfurtkamp]

Speaker efficiency and the preamp etc will have a huge impact on perceived output, same with headroom issues.

If you're planning on the attenuator route anyway, I wouldn't worry about it much.