Gents,
I called tech support (at Bradford White) to understand the BTU vs.
efficiency thing.

Short version (all my brain could hold on to) is the efficiency
numbers all take into account the BTU energy what ever that volume
happens to be... so it is an apples-to-apples comparison to look just
at the Recovery Efficiency (ie 79%) or the Energy Factor (ie .58) from
one unit to the next (of course assuming each has the same gallon
capacity).

HOWEVER... if one unit has 2" of insulation and the next unit has
just 1" of insulation, and they both have the same efficiency
ratings... well the 2" unit is being helped because of its R-factor so
then the 1" unit would have better "blowtorch only" numbers.

Dave-in-Denver