I would be a bit sceptical that the 800 gr Solid would be accurate at all at these velocities. Its been proven time and again that the VLD solids do not like to be driven faster then 3000 fps.
Most are made from brass or some other similiar alloy that will slip the lands of the rifling at velocities higher then this.
I wonder what powder they are using. H-50BMG, US869, VV 20N29 are about perfect for the 50 BMG case capacity along with WC860 and WC872. Thats as slow burning as we can get for powder. Dramatically decreasing the expansion ratio would require a MUCH slower powder to get load densities up to where they should be for good consistant velocities.
I think its more of a gimic round more then anything. Not flaming anyone in any way but I have played with big 50 cals and there is a limit to accuracy as far as velocity. A Mild steel solid may be your best bet but even then, at these velocities, I would be amazed if anything would be accurate by our standards here on LRH.