That is a very false statement. The way a subwoofer plays depends upon many variables, from the sub itself (thiele/small parameters, NOT the size of the sub), to the enclosure its in, to the environment that the enclosure is in (the vehicle).
Also, the Skars are alright on the lows... not exactly low-end monsters though.
Hippo... the price range thing is understandable. If you will build it yourself, or get one built, I will supply you with a design for a ported enclosure for whatever sub/subs you choose to run, unless you decide to run sealed. I'm not the best designer in the world, but I can sure get you much better performance than a pre-fab. Honestly, if you insist on going pre-fab, I'd highly recommend going sealed...
As for the tweets... no clue man lol, my stockers are still in place although they're not being used.