IME if you like the sound of an amp through a cab and you want more, just get a second cab, the same as the first. Then again, I briefly had an Ampeg 115 and an Ampeg 210. I discovered it wasn't my sound, but the band liked it.
I think that cab would explode if you tried to put 400 watts into it. You'd max it out nearer 200 watts. IMO 1 better cab would get you a bigger sound than 2 of these. I'd suggest @FinnDave has a Barefaced Super Twin 212 for sale, or even a single 112 Super Compact would bring another level of sound reproduction.