I would be willing to bet that 50w would be plenty of power. I believe Luke is using ~50w on his, he may be able to give you a review of the bass performance. 40 hz may be a problem, though. They have a fair amount of excursion, but the power will have to be relatively low to allow you to go down to 40 hz.

"If you are flammable and have legs, you are never blocking a fire exit" -Mitch Hedberg