I say go with the sidearm and some super cool optics(like an ACOG!). The EBR's are all too heavy to use and the Karts are usually a money pit.... Plus you could be super cool with your pistol and l33t M4 optics. PS, yes ACOG's can attach to the carry handles, heck with an adapter even Aimpoints can attach to a carry handle. I would also look into the normal 1911a1, the one you listed is their version of the Hi-Cappa. IMO if you can hold both of them, personally I have a better grip with the a1's... But some people like the double stack sized grip.
Its up too you though.
sticks