RE: Sail sizes + power
Do you rig the NP Combat and the Gun MC on the same mast?
It could be that one or the other of your sails "likes" the mast you use in both of them better than the other sail.
You've "not accepted" that the cut and panel depth that each sailmaker so painstakingly figures out for each sail to give the rig the desired amount of power and stability, but it's exactly that, and getting the right mast that can make your sailing balanced and effortless, or unbalanced and difficult.
Saying that the "draught is similar" may give you the idea that the power would be similar as well, but is the draft similar throughout the entire sail, top to bottom, with a similar amount of mast induced "twist" or is the more powerful GUN MC a little tighter in the leech whereas the NP Combat is slightly looser in the leech?
Subtle (possibly unmeasureable) difference in where the draft is placed, both fore/aft and higher/lower in the sail can affect the "feel" of the power a great deal.
If you have individual masts, try switching them and see if the power follows the mast or the sail.
Hope this helps,