Regular cab sub box
#31
#33
8" subs can move faster but that's about it. You cannot compare 4-8" subs to even 2-10" subs as they cannot be compared. The ouput of an 8" sub compared to a 10" sub is not even comparable like a 10-12" sub and yet a 10" is just as tight as an 8". You would need 4-8" subs to equal the output of 2-10" subs and even then you won't hit the low tones as the 10" would or even close to the same output. That's why there aren't many 8" sub guys out there.
I'll have to find the article i was reading that did refer to that. However, i was at my local Car Audio shop last week and the owner who has won numerous sound off awards verified that it was true.
You can compare the amount of air pushed by 10's to 12's, but 8's can only be compared to 6's.
Polyfill will only give you roughly a 10% increase in box volume for what the woofer thinks is there. So a .86cu/ft box with 1/2lb of Poly in each side will yield .86 + .086(polyfill) .946 cu/ft of airspace. Pretty close to 1cu.ft