If you are interested in my two cents worth.
I am our team's XO and armorer and have been working on suppressing some of our team's 10.5 inch entry guns. What I found out is that I can build a gun that runs a suppressor all of the time (on a budget) but have difficulty running one with or without the suppressor (budget is lacking.) I finally gave up and installed the KX3 as a means to divert the muzzel concusion forward and away from the gun as opposed to the side. The reason I gave up on the suppressor is that the gun fouled up very quickly and the backpressure made the gun a bitch to shoot. (even with a Gas Buster). It was neat as a toy, but not something I want to trust my ass to. (One blown primer wedged under my trigger was enough of a warning. Plus, even with a H3 buffer, it was beating the hell out of the hammer.) When I am able to have some R&D funds, I am going to try out Noveske's pinned Switchblock.
I like the KX3 on our SBR's but personally feel that it is a waste on a 16 inch gun. In reference to noise reduction, IT HAS NONE. If it did , BATF would classify it as a suppressor. For patrol and tactical purposes, I do not care for special brakes and rely upon the standard A2 flash suppressors. I recently ran a class for DCIS and one of the participants had a tricked out AR with a muzzle brake (dont' know the brand but look like a miculek.) The side pressure of the gun was UNSAFE and was uncomfortable to the instructors behind the shooter with hearing protection. If you are going to be shooting competively, it may give you an edge (extremely disruptive), but if you are going to be shooting around other officers, save thier hearing. I have also tried other types of brakes on personal guns, but feel that they are a waste of money.
In reference to a light weight forarm, I just built a personal rifle and installed a Troy Industries TRX extreme (13 inch) over a 16 inch barrel. With the light contour barrel, the gun is well ballanced and weighs just under 7 pounds empty. I modified the pinned A2 sight post to fit under the handguard and am extremely pleased. It is light weight; however, you will have to remove the barrel and front sight post. They supply a barrel nut that works with the rail. My department's S&W M&P rilfes also come with Troy's removeable 4 rails. They are also well made and extremmely light and they make a free float version that mounts to a standard barrel nut (cut off the delta ring if you do not want to take off the barrel.)
The rest of the crap is just window dressing. Have fun and buy what you want.
Just be careful pulling your Rock River apart. I have a Varmint A4 and they apparenlty applied lockset to the front gas block and the threads to the free float tube. When I received the rifle, the front sling stud was not indexed correctly for a bi-pod and I was trying to correct it. When I could't get the front gas block or the jam nut loose, I bought a pivoting bi-pod instead.