Unless you find the ACOG sitting too low on the AR upper rail, I don't think the extended rail is going to do you any additional good other than adding more weight to your rifle. I had the ARMS SIR with the ACOG on it, which created the same effect and I found the ACOG is sitting a bit too high for my liking.
I think the rail was design so that the aimpoint can be mounted on it with the low profile mount and still being able to co-witness with the front and back iron sight.