Sheep, don't forget that for a bit more than the cost of a VTF-3 HO, one can get dual VTF-3 Mk3, which would offer some very serious output capability!
As an alternative, adding an MBM-12 to a VTF-3 HO will provide about 10db (!) higher headroom in the mid/upper bass.
Also, the VTF-3 Mk3/HO with turbocharger will move as much air as DUAL -3 Mk3/HO in extended bass mode w/ port plug for a given level of port noise.