In an older Weatherby Guide, perhaps the 50th Anniversary, I recall seeing a photo of a fellow hunting in Africa with what appears to be a 20" braked MK-V .378, which actually appealed to me . . . except for the brake. The Weatherby custom shop, doesn't produce custom rifles in the true sense, since you can't choose different barrel contours or twists, or choose cartridges they aren't tooled up for. But a slick feeding MK-V .378 with a 20" barrel coming in at around 8 pounds, would prove to be a quick handling, flat shooting outfit, that would be exhilarating to shoot . As to cost, not many custom rifles come in under $5K, so these might be considered a deal since it doesn't take months or years of waiting to acquire one. On the downside is the cost of ammunition, and a .375 Ultra produces 95% of the .378's potential, at half the price, even though Remington brass isn't in the same league as Norma.
Downsides, in addition to the cost of ammo, is the lack of a controlled round feed, considered by many to be beneficial on a DGR, the trade off of a lack of camming power for the questionable benefit of a 60 degree bolt lift, and the small magazine capacity. The magazine can be addressed by installing a McMillan stock and Sunnyhill bottom metal, but a lack of camming power is built into the MK-V design. While it won't matter most of the time, under a hot African sun, the rifle might tie up to the point of being unusable if its loaded to its full potential for Canadian hunting conditions. It seems counter intuitive to download your ammo for the biggest, most dangerous game the planet has to offer, but there it is. As a test though, you could leave your ammo on the dash of your truck for a few hours before shooting it on a hot day, then see if your rifle runs with it.