I've about beaten a dead horse with this, but here's what I have FINALLY decided upon doing.
I currently am in possesion of a V-match 16" carbine upper. Since I don't think a perfectly good barrel for shooting Q3131A should go to waste, this is what I will do:
1. Send upper to KKF or someone to have the barrel shaved down to a M4 contour.
2. Remove aluminum handguard and replace with an ARMS 50 SIR OR PRI carbine handguard (whichever is better).
3. Install the KKF "Limiter S" brake.
4. Install a PRI or GG&G flip-up front sight (my current gas block is milled down).
Any more recommendations are welcomed.
I think I should go with the flip-up front sight over a fixed sight just for the sake of using optics. It's already a flattop anyway, and I'll be using an optic 99% of the time anyway.
Also, I'm not sure about the handguard yet. It seems that everyone is pro-SIR. I assume it holds up the best of the bunch, but it seems that a free floated handguard is a more secure way to attach a handguard to a rifle. Am I wrong or paranoid? I just get worried when you have to Loc-Tite a rail onto the flattop, and that's your primary anchor of support for the entire rail.
I decided against a SPR clone because I shoot Q3131A ammo and similiar. I'm too tight nor do I have the time or place to shoot 200+ yard distances with match grade ammo. It's expensive (the ammo), and I really have no perceived need for what a real SPR does at this time. My needs are those of a defense type carbine and just a fun rifle for the range out to 100-200 yards. I just want to improve upon it to reduce its weight and enhance its versatility. I think the configuration above does that pretty well.
Id get a FF RAS over the PRI tube but the SIR reservations are unfounded. It IS a free float tube system and it attaches at the upper and barrel nut. If you are going for an Aimpoint Id get a SIR if you went with a magified optic Id get a FF RAS.