I would strongly recommend standard Colt 6920's for your agency.
The flat top will add a great deal of versitility should you decide to make some sighting changes in the future. Also, anything you mount on those carrying handles will be way too high for a proper cheek weld.
The 16.1" barrel, while not noticably longer to move around with, will provide a bit more of that velocity that is so critical to good ballistic performance from the .223/5.56. While it only provides you with 15-20 yard more effective range with standard Ball ammunition, it, according to Hornady, streches the maximum range of their excellent 75gr. TAP round from 125 yards (14.5" barrel) to 200 yards (16.1" barrel). An often overlooked additional advantage to the 16" barrl is that no special ATF paperwork is required for the agency or individual officer to own these weapons. While it costs the agency nothing to go the NFA route, it does require extra paperwork and it may become a bit of an issue for local officers who transport the weapons across state line for schools and other events. The slight increase in length is worth it.
And while some might disagree, the best current round available for the .223/5.56 is the Hornady 75gr. TAP. Sight in and carry the 75 gr TAP but use Ball for training and quals if cost becomes an issue. POI is within 2" at 50 yards. Standard 55gr. Ball fragments well and is a good round but it's fragmentation is not always reliable or consistant. The 75gr. TAP outperforms it in terms of termianl ballistics, accuracy, and reliable fragmentation.
As far as optics go, you can't do better than the new Aimpoint Comp M2. The battery life is a non issue since it's measured in years under normal conditions. This sight is as end user proof as can be had and it's parallex free design means that it can be zeroed by one person and still remain perfectly zeroed for whoever may use it---it's also very forgiving as far as cheek weld and other things that can get screwy during a raid.
The SureFire 500A is a good system. The only downfall is it's weight but that's about it. If money becomes a concern, the 6 volt SureFire Tactical lights are as viable now as they've always been and they weigh a lot less.
A good long straight sling is also an good addition since it can be quickly put on and doesn't tangle in your gear like a 3 point HK type.