If I'm not mistaken, the 8x75 was one of the calibers offered on the magnum action in original Oberndorf sporters. I believe there is a photo of a rifle in that caliber in Speed's book, as well as images of the cartridge. Original sporters in that caliber are apparently very rare. As to the cartridge, I think the ballistics are something on the order of the .318 WR, maybe a bit hotter. I also seem to remember Speed commenting on a shipment of several rifles in this caliber going to one of the African countries - might be confusing it with something else.