Fi SSD 12 or 15, That is the question

[Ritch40]

Does anyone out here have any real world knowledge of the Fi SSD 12" or 15"?

In a ported setup, what do these like to see each for net volume and port?

I have about 13cuft or so gross to play with.

I would prefer to go with 4 15",but really dont know if in the real world that will be enough space for 4 plus displacements.

Thank you in advance for any information and suggestions.

p.s.

for power i was thinking the sundown 4000