re: Need a ruling on a S&W AR-15.

Since it's almost a given you will probably want to run an optic at some point in the future anyway, I'd go with the OR model. For the $200 price difference you could certainly get a low-end reflex or low-power scope but you'll want to remove the A2 gas block for a low-profile version which, for the quality ones, will make the difference in price a non-issue when all is said and done. Lots of options for iron sights anyway. Get the OR, get an Aimpoint or EOTech on it, have fun then figure out BUIS later.