Huh?
99% of the time if something measures well, it will sound good...
and if it measures poorly, it will sound horrible.
(and by "good" I mean: low THD with/at extended bandwidth and higher-ish SPL.)
Being flat to 1-10hz is one thing. Having enough horses to feel it or make it audible without gross distortion is a whole 'nother level...
The act of measuring is merely another tool, numbers on a page, explicitly nothing more per-se...
Subjectives will always be subjective, hard to validate or invalidate with scientific rigor; hence why they are formally avoided like the plague. (Example: Until we have a "ghost detector" that actually WORKS with 90's confidence, we can't tilt in either direction on the topic, maybe they exist and maybe not. etc etc...)
We HAVE sound detectors though, they are called measurement mics, and they work VERY WELL. Often better than human hearing, and a LOT BETTER than guesswork and opinions.
If the room has a null, or if the box is made of cardboard or if the driver is an 8 vs a 24, it will show differences in the measurements. It will tell you exactly what frequencies, THD and SPL (for a sub in a given spot, for a mic in a given spot...) It will show how close the box-model match reality, especially when measured anechoically or GP outside.
My dual 20hz VBSS’s are on a cheap 500w plate amp and the gain is hardly over half. what would you do?
PA-460's don't like to be ported below ~22hz, the box gets too big and the mid-bass suffers greatly from energy distribution.
Given your budget, I'm not sure what the answer to your question is. My gut says it might be time to add sealed UM-18's if THAT is your true goal (or SI-24's if you really want to burn through the money quicker).
But as was pointed out already, nearfield doesn't get the free room-gain at low frequencies. The reflections need the space/time to actually reflect, for it to add the free db's. So this will make your task more-difficult.
FYI: thought has a t at the end...