it's been years since i've used any dayton's, etc.. so i can't comment on their performance these days. from what i read, it sounds like they've come along ways since i've used them.
my favorite mid bass 6 1/2 right now is the DD W6.5LT. $120 ea, you either have to get them from a dealer or direct from DD.
i haven't tried them ported yet, but a lot of people are raving about how nasty they are in a ported.
IB, it just kept dropping where my mind was telling me "ok, the low end response should be really fading off and about gone by now". the flip side is.... use it as a mid bass in a 3 way. what it does play of the mid range it does good, but it doesn't go up very high. i'd run it up to about 500hz +/- even though it will go up to about 2k.
and brace the heck out of where ever you mount them. or else you will lose a lot of energy into panel flex. they're pretty explosive and violent when you lay the power to them with rippy mid bass.