Unless the locations for the subs are predetermined without much wiggle room, I think that size/weight does make a difference, because in order to optimize performance, placement experimentation is absolutely necessary. That means moving the sub, a lot. And if you are throwing down around two to three thousand per sub, you are going to want to get the most out of them. Some of the subs you mentioned can not be lifted by a single person, period, not even if you are a body-builder.
As for running duals of these things off of a single 20-amp circuit, yes, that can be done, if you never take advantage of their headroom. But if that is the case, why get a monster sub? I have had a 1.5 kilowatt RMS sub dim my lights when they were one the same circuit as a light fixture. Peak power draw is already much higher than RMS power draw on these subs, at least twice as high.
As for three VTF-3 mk5s vs the $2500 subs you mentioned, it would not be a fair fight; the VTF-3 mk5s would have a major output advantage across the board at 20 Hz and above. One of the reasons for this is because size equals efficiency, and three VTF-3s do occupy a greater volumetric area. I don't know how much more most people would feel the need to upgrade, because three VTF-3s would probably give you 120dB+ in-room at 20 Hz and above.[/QUOTE