G'day Tony,
Most of the lads shooting the larger boars in Australia are using about 60# at the least, and shooting at least 600 grains with two-bladers. A few fellows are successful with lighter bows in the 50# range, and one really good hunter used to shoot a few big boars with a high 40# bow. And a few fellows do use three-bladers, although one of the lads who used-to use them quite often has switched to two-bladers in recent years.
The whole debate centres on what is possible as opposed to what is best practice, and is quite similar to the issue of smaller calibres for buffalo possibly working very well as opposed to larger calibres absolutely working well.
I've killed big boars with 83# of Silvertip and ~750 grain, STOS-tipped arrows; 78# of Hill longbow and ~700 grain, STOS-tipped arrows; 78# of Black Widow longbow and ~700 grain, Magnus II-tipped arrows (and one fair boar with a Woodsman).
I don't believe that the weights above are vital for big boars at all; but they certainly work well.
So far, I haven't killed a big pig with lighter bow, but these days I am shooting bows in the 60# range.
Cheers,
Ben