Moving from a VTF-2 to a Monolith 12 is too lateral of a move, in my opinion. The Monolith 12" is a higher performing sub, but not massively so. I would set your sights higher in an upgrade. Look at the 15"s from Hsu or the Monolith 15". The Outlaw X13 or SVS 3000s should be a significant upgrade as well, and also the Paradigm Defiance X12.