To be honest, my Valve Junior doesn't sound much louder when hooked up to a 4x12". Maybe a little bit, but not an extreme amount.

It does, however, make the sound 100x better.
Main gear (For complete list, see profile):
Epiphone Les Paul Standard Plain-top
Basswood Telecaster, 2 single-sized HB's, both split.
Epiphone Valve Junior
B-52 AT-412 Cabinet
Oh, and I have a Squier VM Jazz Bass too.