I am tempted to go with an A1 upper for weight savings and simplicity.  I understand that the Canadians went with an A1 upper and an A2 aperature.

http://www.sfu.ca/casr/101-c8.htm

What aperature works best with a forward mounted rail optic in case I want to go that route later.  From what I understand:

A1 aperature, both holes are the same size.  One is slightly higher for extended ranges.

A2 aperature, one hole is much larger for quick aquisition, other is smaller for precision.  However, they both hit same POI?

Anyway, any opinions?  I am thinking of a lightweight 16" barrel with A1 upper and M4 stock.  The CAR stock just looks too 70's...

A1 is fine, add ashley outdoors same plane apertures and zero for 200m.

so even A2 aperatures are not on the same plane?

Quoted: so even A2 aperatures are not on the same plane?

Nope, they are off.

Quoted: A1 aperature, both holes are the same size.  One is slightly higher for extended ranges.

Correct

A2 aperature, one hole is much larger for quick aquisition, other is smaller for precision.  However, they both hit same POI?

Partially incorrect.  The holes are a different size - but they hit to different points of aim (from 2-4 moa difference).

Anyway, any opinions?  I am thinking of a lightweight 16" barrel with A1 upper and M4 stock.  The CAR stock just looks too 70's...

Great Configuration.

For an aperture get the Express Sights same plane rear aperture.  Two different sizes like the A2 - but they both hit to the same point of aim when you flip between them.  The apertures are both a bit larger than the standard A2 apertures as it's designed to work with Expresses fat AR15 front sight.

so with an A2 sight setup, when do you start using elevation knobs vs. flipping the aperature when you want to go long range shooting...

Quoted: so with an A2 sight setup, when do you start using elevation knobs vs. flipping the aperature when you want to go long range shooting...

You zero at 250 or 300m, then flip to the large ap for 0-200m. At longer than 300, you use the small ap and the range dial.

Somebody correct me if I am wrong, I never use the range comp feature on my sights, so I'm not totally up on it.