I prefer the 1/7 twist in 223's because I like the way 77gr Sierra's shoot. They shoot quite well in my 556 Classic. A 1/7 will still shoot 55's ok but most of my 223 shooting is done with 69-80gr bullets.
As far as Optics go, my favorite for the 556 is an Aimpoint M-4. Battery life is incredible, one single AA battery and you can pretty much leave it on for 5 or 6 YEARS and not have it run out.
The biggest thing you want to watch for on a 556 Optic is the mount. I also like Eotech sites but they overhang the rail enough to where they interfere with the bolt handle. Get an optic that the mount isn't much wider than the rail. I haven't had a Trijicon yet but they might be a good choice if you want a little magnification, but mine all have aimpoints of one flavor or another................................DJ
