I use a single pin Impact Jumbo sight, with a 6" extention bar.
I sight it in for 25 yards...I'm alittle high at 20yard(1.5") and about 2" low at 30. I shoot a Guardian witha 416grain arrow @ 282fps. I imagine with an allegiance, you would have even less of a drop.

I have also been hearing good things about single pin slider sights. I know mobow like his.