Full Curl,
One thing to consider regarding M700 actions, rails and rings:
Often the factory drilled and tapped scope mounting holes are a touch out of alignment. This is something your gunsmith should check before committing to a new base, angled or not. If he finds that the holes are out of alignment, then I suggest moving to the next size hole and threads, #8-32. These are slightly larger in diameter than the factory holes so the new holes can be done correctly while cleaning up the out of alignment factory holes.
Another point to check is the alignment of the front ring with the rear ring. While we know they are not on the same plane, sometimes they are slightly different even with the correct height adjustment on the rear ring. This will put a slight bow in the rail if using a 1-piece rail and put stress on the scope tube with either this or the 2-piece mounts.
I use 1-piece rails with a built-in 20 MOA nearly all the time because of the ranges I build for and the simplicity of the system. Given your potential for 800 yards, I think this is a no-brainer.
Here is a brief visual summary of mounting solutions used by the top PRS shooters:
I have used and will continue to use, any of the top 6 makers in this list. I have a definite leaning towards the Spuhr mounts but only if the budget and weight allow. They are expensive and they can have significant weight if you don't allow for it. But once you use them, it's hard to go back to the others.
Regards.