GSP/Brit cross...
Though I would never encourage anyone to do this intentionally, due to the reasons already stated, my favorite dog was a GSP/Brit cross. He didn't run as big as my current GSP, he wasn't as durable as my former brits, but he was the best overall "bird dog" I've ever had. What made him the best was his disposition. When Grampa's GSP climbed the fence and knocked up his brit, gramps said he was gonna shoot 'em all. Instead, much like the Charlotte's Web story, the 12yo Chad begged him not to put them down. I remember him saying, "If your dad is willing to take the chance that's fine by me, but nobody's going to want these damn things..."
Boy, was he wrong. My other grampa just so happened to have had a couple of accidental breedings of the same mix, so he had a network of buddies for me to call. All of the pups, except the 2 my mom and I agreed to keep, were placed in home immediately. 2 of the pups went to homes of men that were long in the tooth and physically incapable of hunting anymore. They simply wanted them for pets b/c of the ones they'd got from the 2nd grampa mentioned above, long ago. 1 of the dogs we kept ended up being my closest ever K9 companion, the other my mom's best friend (gun shy). The dog knew more tricks than a street corner hustler
So, while I believe most of what was said in response to your original post Jethro, I also understand why you'd believe that having a cross-bred litter of pups would be a treat. I'd certainly take a GSP/brit cross from a genuinely accidental breeding, but I'd have to more thinking on the subject before I could take one out of a litter that was intentionally bred that way...I've never known anyone that did this intentionally, just a few "good ole' boys" from KS who had a breeding occur due to a hole in the fence, or a few minutes of hokey-pokey going undetected in a CRP field or whatever.
Either way, good luck finding what you're looking for, but please, make sure they all have good homes before you end up with 4-8 pups on your hands.
If I can find a digital picture of my beloved mutt "Beethoven" (after the composer, not the movie), I'll be sure to post it. He had the hair and legs of a GSP, but the body of a brit (more round and stubby than long and lean). His coat was a lighter color than what I'd consider the typical GSP. He and his brother were the most intelligent dogs I've ever had the privilege of "owning". Dangit...I sure do miss my buddy