Well, to make it simple, let's take a starting point of 50 WAR, unimproved. Assume 100 skill with no other perks or effects, no shield equipped. This example is also assuming that the NPC likewise has an armor skill of 100.
You - 50*1.4*2=140
NPC - 50*2.5*1=125
If you reduce your perks to 4/5 for an 80% increase, you would come up with:
50*1.4*1.8=126
So it seems like the increased coefficient is equal to about 4 perk points.
Interestingly, I did a little surfing when making the assumption above that the comparison NPC would have the same skill and came across some good information about NPC characters and their determined stats and ability to increase those here -
http://www.uesp.net/wiki/Skyrim:Classes A lot of good information there in the NPC section about values that govern their behavior as well. If you further investigate individual NPCS, you will find that a good many of them DO have perks, so the premise I believe you were exploring in another thread about playing without perks to limit yourself to the same capabilities as NPCS is not necessarily the case.
Edit: I fixed the calculation on the 4/5 example. The first time I actually reduced the armor skill to 80 and left perks at 5/5, resulting in a value of 112.