Oh yeah I did read your post about scoring on the Noveske! Congrats, that's one fine rifle! And it comes with a milspec BCG so you'll have it to compare to whatever BCG you end up with. Hope you can also score the DD BCG, I like the one I got 2.5 years ago.
In a pinch you could borrow the Noveske BCG to test your new upper.
Yeah it's not a bad idea to have a backup BCG but every spare I've had has morphed into another AR instead.