Boston T. Party backs up your opinion on the value of Body Armor – to quote: “… An order of magnitude advantage” (“Boston on Surviving Y2K and Other Lovely Disasters“).
you posted a good letter from Ryan that mentioned adjusting your buttstock length to account for Body Armor, web gear, etc. The main point to test all your gear – all at the same time – is a real nugget of wisdom. It’s amazing the glitches that pop up that you can never foresee until you test.
One thing to note – 2″ is probably a little too much compensation in buttstock length unless you have very thick clothing and web gear as well. Ultra-light Polyethylene Rifle Plates are just under an inch thick (~2.5 cm.) but the most protective Level IV Ceramic Rifle Plates are only 0.75″ (~2 cm). So an inch of adjustment with web gear is probably a good estimate.
We offer both Ultra-light Polyethylene and Ceramic Rifle Plates with a “shooters cut” on the Front plate. So, with this taper at the top of the plate, you can get a buttstock plant directly onto your body (or soft armor). See this photo page . So you would have just 0.25″ (~6mm) of soft Body Armor under the buttstock with “shooters cut” plates.
Yours Truly, – Nick – Manager, BulletProofME.com  Body Armor
JWR Adds: My approach at compensating for the thickness of body armor and/or heavy winter clothing is as follows: Size your buttstock with assumption that it will be used in conjunction with body armor or heavy winter clothing. Then, in instances where you are shooting in casual circumstances without body armor (or in warm weather), simply add a slip-on recoil pad  to make up for the difference in stock length. That pad can be removed in seconds, if circumstances change.
For any readers with HK91 s or CETME s (or clones thereof), I recommend that you buy a couple of inexpensive spare military surplus G3 stock sets s from Cheaper Than Dirt . They currently have G3 stock sets on sale for under $10, complete with a pair of handguards and a pistol grip! (See item # MGR-281 in their latest catalog.) With a price like that, you can afford to buy several stock sets and get creative. Do some WECSOG  experiments with a hacksaw, two-part epoxy, and various recoil pads–while of course saving your original stock in its original configuration. OBTW, I am not a fan of the G3 “A3” collapsing stock, since it has a buttpad that is uncomfortably small and curved, and its stock rails do not provide a consistent cheek weld . An A3 stock might be useful in confined spaces (such as defending a vehicle), but otherwise, I do not recommend them.
For any readers with M1A s, I recommend that you buy a few inexpensive spare stocks from Fred’s M14 Stocks –they have thousands of M14  stocks in inventory–and shorten them as needed, adding recoil pads in the process. OBTW, I am particularly fond of the Pachmayr “Decelerator” recoil pad . One of your spare stocks should be cut extra short, to accommodate any small-statured shooters at your retreat. Just keep in mind that when you switch stocks on an M1A or M14 that it may have to be re-zeroed. Test your rifle’s accuracy with each of your spare stocks well in advance of Schumeresque  times.
For any readers with AR-15 s or AR-10 s, I recommend that you buy a complete spare collapsing (CAR-15 /M4  Carbine style) buttstock assembly. You should preferably one that has three or four adjusting “position” notches. For fine-tuning the length of pull, someone skilled with a drill press can add additional adjustment notches.
We use L1A1 s here at the ranch, three of which are equipped with extra short length-of-pull “Arctic” Maranyl stocks. These stocks were used extensively by the British Army in Northern Ireland in the 1970s, where they wore body armor for foot patrols in inimical places like Ulster and Belfast. Thankfully, L1A1 buttstocks have hard plastic pads that come in several lengths, although changing them is a bit time consuming, since the recoil spring nut must be removed. Arctic length Maranyl stocks can occasionally be found on eBay. Unfortunately, metric FAL s–at least “as issued”–do not have as much stock length flexibility as L1A1s. However, as with an HK91, you can buy a couple spare stocks and do some WECSOG experimenting. The limitation, however, is the protruding recoil spring tube.