trying to find good medium/ long range optics for AR-15...

[USCG]

I am picking up an AR tomorrow, and I am trying to do some research on what would be the best optics for a bit of distance, it comes with a JP super match barrel, so it has a fair amount of reach, I would like to be able to comfortably reach 300-400 yds (maybe a little bit more since our local range reaches 600 yds.) my main concerns are:
-what kind of magnification should i look at?
-what gives me the best bang for the buck?
-what is the best mount?

I am also looking at putting a small red dot either mounted on the scope, or at a 45 to the scope for short range.

I have looked at the:
-trijicon ACOGs (a bit pricey)
-trijicon accupoint 3-9 or 2.5-10
-leupold mark 4 CQ/t 1-3x
-leupold mark AR 3-9x or 4-12x
-leupold mark 4 LR/T 3.5-10x
-KonusPro M30 3-12

I am open to any other suggestions...

[Bartholomew Roberts]

This is an article that is worth your time to read:
http://demigodllc.com/articles/fighting-carbine-optics-short-guide/

I'd also recommend just generally reading some of Zak Smith's thoughts on various optics here: http://demigodllc.com/articles/

[GAR700]

I put nikon on my AR and it worked wonderfully. The BDC reticle is set up well for 223. I also had a 3.5-10X Luepold VariX III on it for a while but the nikon fit it better.
Good luck!
GAR