AR's, hmmmm....
Here are my opinions and suggestions take them for what they are worth.
S&W does not have much history with AR's. I think they are over priced.
If you want to drop serious cash on an AR get a Rock River.
Bushmaster is another good one for dependablity.
You can get "custom" AR's for about the same price. Look around. AR15.com is a good site to check out.
As far as the sights go. They make quick detachable scope mounts for AR's that reattach with little or no readjsutment on zero hold, assuming you are not a competitor and demand ultimate accuracy.
They make AR's in many different calibers. 223/5.56, 243 WSSM, 25 WSSM, 6.5 Grendle, 50 beowolf, 458 socom. etc....
How far can you shoot them?
How far can you shoot a 223 Rem?
many competitors shoot their 223 AR's at 600 yards. Far enough for you?
I have a stock Colt 223, and with practice and the right ammo I could confidenly hit a pie plate at 300 yards with open sights.
AR's are a world unto themselves. You can go as deep as you want.
I have "built" mearly assembled 3 AR's myself. Fun and easy.
If you want high accuracy and are willing to pay, look for an AR from Rock River Arms.