I think Alex's point is that while the amp will put out fewer watts you can get back much of your "lost" SPL because the cab is pretty sensitive.
I know I ran a Berg CN212 with my TH500 with both volumes at 12 o'clock but now I'm running 2 Super Compacts I have to dial the master back to just over 9 o'clock.
I get what you're saying but it doesn't exactly address my issue (not really an "issue" though as I am satisfied it can all work fine).
I realize that BF cabs are good cabs with good sensitivity, as I own three (BB2, Four10, One10.) However none of those I own are 12 ohm. I am comparing apples to apples -- BF cab to BF cab-- and the 12 ohm model will produces 2/3 of the power of an 8 ohm (of which there is no 8 ohm Two10) and even less by comparison to the 4 ohm model Two10. Comparing them to lesser cabs which they can beat the pants off of even with higher impedance-- doesn't change the 2/3 ratio for BF cabs. As I mentioned, 12 ohms out of my MB 200 is only 93 watts. The min recommended power for a Two10 is 100W. My TH350 will give me 117 watts, which is marginally above the min. recommended power So, it's not as though there are no potentially tangible effects (for me) of running a 12 ohm cab by itself.
However, after some thought yesterday, I have concluded that, for me, this is not an issue since I can bring the MBF800 which will give me 268 watts into a 12 ohm cab-- right in the middle of its recommended range. Yes, it's a little bigger than the MB200 or TH350, but not by that much.
Realistically, for me right now, I don't need more than a Four 10 or a BB2 as stand-alone cabs (they are so sensitive!), for most mid-to-high volume gigs (One10 still great for small stuff). Someday, ideally, it would be nice to have a 12-ohm Two10 cab (to use stand-alone or as an add-on to the Four10) and a Super Midget (to use as standalone or as an add-on to the BB2) for outdoor stuff where PA support may be lacking or non-existent. These are on my "eventual" list, if I live long enough to "eventually" do it.
Four10, BTW, has 38% more speaker cone area than a Big Twin or Super Twin. It's a beast.