Brian I think a lot of the CG data originates from BC's measured by Harry Fuller? It gives a general idea about a pellet but actual values can be quite different.
As Colin pointed out above, many people don't run 8.4's close to the limit as I too have found they are better at around 780 fps, and also like Colin when I was using the heavies I found they were at their best when pushed as fast as you dare set the rifle which does minimise a little of the trajectory difference.
As to a pellets bc performance difference between regged and unregged, I believe there is a difference. it is not the regulator itself that makes the difference but the pressure used to fire the pellet.
In this graph of a shot string from an unregged rifle you can see that when the cylinder pressure is high which would create a short duration to the firing valve open time the bc is higher, as the pressure comes down and the unregged action automatically compensates with a longer valve duration the bc gets lower.
I am sure the velocity also plays a part here, the higher velocity causes greater drag which lowers the bc, this may explain the rise in bc value towards the end of the string as the velocity drops.
Graph originally from Harry.
So if we knew the res pressure around shots 8,9 and 10 we could build a regulated action to run at this pressure to achieve the best performance from that pellet at that velocity in that rifle. I have been working in this area for a couple of years but have so far failed to convince any manufacturer that better than what they are selling us is possible! I believe massive gains in rifle external ballistic performance is possible with proper development. Instead we get useless cosmetic changes between rifle models!