I've owned the walkabout and currently gigging the v4 with the 212 av cab. Hard to say. The walkabout I only played as a 15 combo. The cabs will have a lot of effect on the tone and volume. The Ampeg 4x10, although I have never gigged one, is known for going real low and some say get muddy. I have no experience with that cab though, so can't say if that was a factor in what you experienced or not.
I can't say enough good things about the v4 and 212 combination. I use mine in a 3 piece rock band and a 4 piece country band. It is more than enough for both bands withe the master dimed and the gain around 10 maybe approaching noon depending the venue and drummer. Loud is subjective. To me if I dime the master and turn the gain to noon or above, it's real loud.
My guess is the walkabout would give you more clean headroom but not nesasarily be louder than the v4 can be.
If it were me, based on my experience with both amp, all be it with different cabs. Hands down I would go with the v4. Although thru the mesa cabs you may have a different experience than I'm having with Ampeg 212.
If $ is not the main factor I would go v4 212 Av cab. If that is not enough you could add another matching 212. I can't image with two 212 cabs you couldn't get loud and clean enough.
If $ is a big factor. You already have the mesa cabs. You could get the head to try it with your cabs. If it's not enough the v4 does 2ohms, you could add more cabs.
Or you could do the reasonable thing and buy a used walkabout off the classifieds for about $550 or so and see if it floats your boat and be done.
