You could just put him on any base really, as long as you can put a lot of detail on it, because it has some very tasty advantages, such as being in base contact with more models, so more blood to spill. I modelled my Luthor Harkon on a monster base, not only for the extra base contact, but to fit in properly with my zombie ogres.
Heres an example of getting the most out of bigger bases: Take a chaos lord level model, give him the berzerker sword and something like a ward save to give him some kind of protection. Stick him on a mount, so your opponent won't be complaining that you just gave him a really big base, I would use the new HE plastic dragon, model it turning so much that the whole model is looking from the longest side of the base (which is 90 deg from the one shown on the box, so just have the head turning and the wings in a different position. With a berzerker sword, he'll cause a lot of destruction, espesially on the flank.
Bigger Bases are well worth it!!!! Because Its LEGAL!!!! Mhu hu ha ha ha!