I would definately get a Saddleback Boar. But make sure and get one from a different bloodline to your own.
When Gloucestershire Old SPots have piglets from a saddleback boar, they are usually saddleback piglets, sometimes they may have a spot in their stripe - but at least your herd will look good, and if there only for meat the spots in the saddle will not matter. Also you have more Saddlebacks than GOS so it would make sense.
Its a personal choice really if you never intend to sell piglets, but if you might want to sell some piglets, and you have the chance to register your new weaners, I would, then you have the best of both worlds. Buy a Registered boar too, you will just have to have a different tagging system for the GOS weaners so that you do not make the mistake of selling one of her weaners thinking that it is a pedigree saddleback. We have different tag numbers for different breeds. It is important to do this for the records and future of Rare Breed Pigs.
Again - if its only for meat the animal husbandry is simpler, good luck with the piglets - your gonna have some laughs and lots of fun x