Well, I finished both of the 520s and cannot be happier.
I took them to the range for testing with a bud of mine and after he fired my first build he said he had to have it so he bought it from me (I will keep the second build for myself). We ran both on 00B until we got sore. Shooting with the trigger held down is very fast once you get used to it. The first shot likes to make the guns automatically cycle the second round just using recoil so you have to hang on with a firm grip or this will surprise you the first few times.
Now that the testing is over, I will find a nice military sling for it and call it good.
BTW the Duracoat "Parker" finish is a dark grey Parkerized look that really fits well with these.