I ran the numbers. To get 6.5 mils out of the 800 grain requires 3050fps. At 2850 your holding 37 mils. To match up to the .375s you would need to push 3050fps. Hornady AMAX would need 2900fps.
Out of the rifle requirements for barrel and other parameters you are looking closer at around 2300 - 2400 FPS. Which would give you the following for the .50 BMG under the new requirements:
1000 meters = 12 mils
2000 meters = 37 mils
2500 meters = 57 mils.
You are not going to get even close to 2800 fps if you follow the project guidelines for weight, barrel length, and other aspects.
.375 EnABELR has already been selected as the replacement, after years of success at this point down range. It proved to be a better option. The only question now is who will build the new rifle, and what will the final design look like. We don't have a dog in this race either way so it is exciting to get to sit back and watch what they come up with.