There is debate over whether or not the old boars are worth it:
http://thefiringline.com/forums/showthread.php?t=449963
I think another issue is, how do you move a 400Lb boar? It's a lot of work. A lot of work to field dress them, a lot of meat to haul... and it sounds like a lot of work to make them taste good.
Why bother? Just take a 200 sow.