Hi Tiim,
The 7B still has almost twice the capacitance per channel of a 14B. The more difficult the load the more the 7B SST2 makes sense over the 14B. Placing an amplifier close to the speaker is also an advantage.
With normal loads and normal listening levels the 14B is all you would ever need in most setups. That is why I usually say that the choice is more one of Application rather than Performance. 
james
Hi James,
thanks for that confirmation, i guess if i'd known at the time i would have gone for four 7s instead of the two 14s.
In reality the the 14s sound so good right up to full power into the BB5is that i'm not going to lose any sleep.
95Dyna,
i don't think i'm presented with that nasty a load, 0.8 Ohms is a tad extreme. Nominal 4 to 5 Ohms but in biamp mode (crossover in the preamp)
maybe a bit higher esp on the treble / mid.
Had Tortoise / TNT on last night and the system renders it so well.
Not too worried about the weight of the 14Bs; it took four of us to lift the speakers onto the stands though!
Have a good weekend
Tim