Duke, I want to make sure that I understand you correctly: Are you saying that a 4 Ohm 1203 would have less low-end beef/extension than the 8 Ohm version? I was thinking a 4 Ohm version might go nicely with my Walkabout. I do feel tied down by that amp's 300W @ 4 Ohms/ 165W @ 8 Ohms power rating (though it'll reportedly do 450+ @ 2 Ohms), but I have, finally (after trying different tubes and rethinking the EQ), got it dialed in and sounding soooo good... at least at home.

I haven't had it out for awhile, but want to, soon (just got an fDeck Series III hpf to go with it). I do have bigger (and costlier) amps with more juice, but if I could get the volume I want out of this, with the same feel, dynamic range, and clarity I've got now at low volume, I could see several pieces of gear going.
If the 4 Ohm version simply has a different response curve but can get the same extension/sound with a bit more low-end EQ, that doesn't seem a big deal. If it actually has less low-end handling/extension, then maybe not...
I know that one could always use two cabs, but it would be nice to be able to use one at something approaching its potential (though I would then be limited to using the one 1203 with any of my digital heads, which only go down to 4 Ohms).