I would echo alot of what Pro2 has said. The TA11(x) is a most excellent optic (Trijicon's finest, IMHO), and reticle selection is sort of a speed-versus-precision consideration.
My first ACOG is an 11F [red chevron]; I like it just fine for speed, but it is not what I would consider a "precision" reticle. Having subsequently tried the donut in 31 & 33's, it seems a bit more intuitive than the chevron for maximum speed, but arguably even less of a "precision" reticle.
I bought an 11J [red crosshair] earlier this year for daylight use on my suppressed 6.8 SBR hog gun, and couldn't be more pleased. While it is not quite as "fast" as the chevron or donut, it does allow very precise shot placement, and is thus quite suitable for my intended application of that platform. During a recent T&E session using a PVS-22 with the two ACOGs, the crosshair was clearly superior to the chevron, but that is a substantially specialized application involving $10k worth of optics.
Lots of folks rave on the horseshoe; I don't have enough experience with them to comment. I have also never tried the triangle or circle/chevron.
One other thing to remember is that once one gets into stadia line ranges, the "base" reticle really doesn't matter much.
Alot of folks also rave on the green. I have stuck with red, since I have several AP's, as well as red illuminated conventional scopes [NXS's, Leupy's], and prefer the consitency. I do use the amber reticle versus red with my D-740 though, but that is a substantially different application, what with the green screen and minimizing eye fatigue in the night environment.
As far as the "piggyback" RMR goes, you really should try it first before spending the $$$. To me, the chinweld would be intolerable, but YMMV. If you are dead set on having a red dot to supplement the ACOG, which I personally find superfluous, you may want to try some of the "cant" mounts such as DD, LT, TNVC, etc. It is also most beneficial to try out as many ACOGs as possible firsthand before buying. They are great devices but some folks get "surprised" for various reasons the first time that they look through one...or a different model.
One last comment, if you are cross-eye dominant, BAC might not work particularly well. I am heavily right eye dominant, and when I mount my ACOG'd weapons left handed, the sight image that I see is an unmagnified one with the reticle floating out in space to the right of the optic. If I close the right eye, the image is clear through the left, but there is a significant POI shift. Again, YMMV.
Hope this helps.