Yes 30 or 40 corsairs with FC works very well. The Amount of attacks you get is amazing with the addition of Hatred and any other special rules granted by heroes, Lords, etc. I have seen them in play and they hold a fight. The advantage of taking 40 would be that you would gain all your attacks 1,2,3 ranks and have the 4th as a backup incase you fail some saves, eg, Your (I) is lower than the unit you are facing so you strike last, you loose 5 men, that are taken from back rank, you attack back with full attacks as you didnt loose anymen from 3rd rank. Although doing this is expensive, points wise. It really depends how many points your willing to spend on one unit and what advantages the unit would have on the rest of your army.
Hope this helps, happy gaming =)