It really sucks that surefire discontinued their reflex 5.56 cans. I hope that AAC holds on to the SPR-M4. Johnson, that's an extremely well thought out rifle and exactly what I am going to do with mine except I'll be using the standard MK18 rail with flip up BUIS or the centurion HK BUIS and an AAC SPR-M4. I found a place that stocks the SPR-M4 muzzle brakes so I'm going to jump on it as soon as my trust is ready.

EDIT: your rifle is pretty tempting Johnson, part of me wants to go with the FSB and the other part doesn't. If I go with a non FSB I'm really leaning towards the Centurion Arms HK sights.