I shot a 60 lb Allegiance with a 381 grain arrow at a speed of 272 fps with speed mods at 28". Your arrows weighs 80 grains heavier divided by 3 for each 1 fps of speed loss, so it should shoot your arrow at, 246 fps.... just like K-Zone comes up with.

My 70lb Allegiance shoots my same 381 grain arrow at 305.