We do lots of crossing. We have saddleback and GOS boars, to breed with their respective halves, but as we have large black, large white, berkshire, tamworth, KK, landrace, OSB and just got a Mangalitza, we cross-breed these to our SB and GOS boars.
The results are some really interesting markings, and in many cases you get what is called Hybrid Vigour, that is the young grow faster than either pure strain would.
Favorite of ours is SB boar X Landrace, stonking piglets! A friend swears by large white boar to large black mum.
Yes we need to keep the purebreds going (and we try to do our bit with SB and GOS), but crosses are also great fun, and taste just as good !