Zen-lite for midrange-speaker with IRFP 250


I want to build a ZEN-lite for driving a midrange speaker from 200 Hz - 1.500 Hz. I want to use a 80 Volt rail for an output of 20 Watts/ch.
For this application, which MOSFET is the best?
I would like to use the IRFP 250, because the THD from 200 Hz to 1.500 Hz is very low and it seems to be no problem to run this Mosfet with 80 Volts. Or is it better to use the IRFP 140?

Is the damping factor with the IRFP 250 lower as with the IRFP 140?

With amout of power must I dissipate with a heat sink?