Weatherby loads Hammer Hunter 185 grainers so I would switch to that for a factory set up. The ammo is about $100 a box and runs 3,100 feet per second from the 24" barrel. I saw it on a few web sights.
The 8mm wildcat exists only in my mind. (Maybe nest year it will be a reality.) I expect the Hammer Hunter 198 grainers would have a velocity of about 3,300 feet per second. Its estimated G7 B.C. is .248. I had a 28" barrel installed on my .375 and also installed a brake on it. I used it for one whole season in Western Oregon to see if its longer than normal length would catch on a branch or anything. During the five weeks, it hit one branch. Therefore, the 8 wildcat would sport a 28" barrel with a big brake. I have no idea what Allen Magnum is charging for his 7mm brass. It's based on the .338 Lapua Magnum improved, so expect it's a pile of $tens to get 100 cases. Allen magnums are readily available, so I presume the brass cases are also.
Presently I have an 8mm wildcat that looks like a 7 Weatherby necked up. I use Norma 7 Rem Mag brass with the belts turned off and the rims machined to fit the small six lug Weatherby. I fire the Hunter Hunter 198's from its 24" barrel at 3,054 feet per second. Over the years it has proven to be a great game getter. The scope weighs 22 ounces and brings the loaded weight to 7 pounds read to kill.