In possibly the luckiest thing to happen to me, i won an ICS M16A4 in a raffle at Op. Shahrazad in 2014. It sat around, collecting dust for the most part, until i just decided i wanted a Block II M4A1. Not to go with any loadout, but because i just did.
I bought the 14.5\" barrel and the rail set and got to work. I had a spare M68 Aimpoint, and knowing that it is a kosher optic for SOPMOD M4s, i was satisfied. On the list is a PEQ-15 and a M3X. Possibly replacing the Aimpoint with an EoTech 556 or a SpecterDR.