Like you, I am also concerned about over-penetration. There are lots of theories out there, but some great real world testing has been done here...
http://www.theboxotruth.com/docs/theboxotruth.htmYou might want to nose around a bit in the forum section there too. Some very knowledgable folks including ER surgeons, ballistics experts and others.
As for Speedfeed stocks... they are simply an excellent aftermarket stock that integrate a nice recoil pad. Personally I don't like the slip-on pads for HD simply because I am paranoid and worry that it won't stay put. Probably silly on my part. -shrug- Also these stocks are very well made and fit like a glove on Remington and Mossberg. Super easy.
NOTE: Speedfeed has a model (Speedfeed I) that holds 4 extra rounds in the stock itself. Lots of folks like having spare ammo on hand and this is a sleek way of doing that instead of a protruding 5 shot "side sadddle" that bolts on the gun.
http://www.speedfeedinc.com/products.htmlAs for the SureFire... I believe this is the one "accessory" that really is needed for a HD shotgun. There is so much tacti-cool crap that can be bought and most of does nothing; or worse can cause problems! But a good weaponlight is a whole different thing.
I've posted in another thread on this, but it comes down to this fact. Hopefully it will never happen, but if it does you pick up a weapon that has the power to kill a human being. And other humans including kids hidden behind walls, neighbors, etc. I DARN sure want to see what I am aiming at at 3 AM in the morning with my heart pounding, scared to death for myself and my family. There is no "oops" when it comes to deadly force.
With shotguns, it's nearly impossible use a handheld light and the gun at the same time (yes I know some LEOs say it can be done). And again, bolt-on type items run the risk of getting snagged and/or fumbling with switches etc. No time for that. So the SureFire front end integrates right onto the gun. Rugged as heck (made to the vibrations of weapon fire), always there, instant-on switch right where it should be. It's the elegant solution.
http://www.surefire.com/Mossberg590500Is the light expensive? Yup. But IMHO, if push came to shove and you only get one thing, this is it.
Hope this helps and keep up with the training,