i had no problems getting numbers outta memphis subwoofers. you can do mid 140's with a pair of 12's or 15's, provided its in the right setup, with proper amounts of power going to the woofers.
i would similarize them with power acoustik mofos, but mephis is better than power acoustik. 70~80 SPL \\ 30~20 SQ id imagine. im getting a mofo15 this or next week in the mail for my friends setup.
I am currently running two memphis hpo 12's which is a pretty low end memphis sub. They are running off a directed 2400 about 700 watts. I am doing mid to low 140's with them I love them.