What are the pros and cons of each version.

I have be looking at the ARMS 40L and I am still a little undecided about the same plane or standard model.

I think the standard just has a larger windage knob so it does not sit as low folded up..   The 40L v.s. SP, it is my understanding the two appatures on the L are not in the same plane so you can get a little more elev on the small apature for longer range...

L = lower profile and small apt. is default
std = taller profile when folded and large apt is default

Sorry guys, my question may have been a little confusing.

I do think I want the 40L.

Doesn't ARMS offer a same plane aperature option on the 40L?

That's what my question was intended to be, regarding  40L standard configuration and 40L with same plane option.

I realize the small aperature on a standard sight is intended for long range and is set higher.

I am wondering what exactly the purpose of the same plane aperature setup is.

GOOD? BAD? ??? Opinions??

The A2 apertures have the large and small offset so that the POI changes when flipping between the two.  (Supposedly for 300m on the small and 200m on the large.)  The 40L retains that, while the 40L SP has the two on the same plane so the POI doesn't change when switching back and forth.

IMHO the same-plane is the better option because you're going to be using a BUIS at close range and not adjusting for distance.  Just set it for the 50y/200m IBSZ and hold COM at anything out to 250yds.  Use the two sizes to adjust for speed/precision or lighting conditions.  

Quoted: The A2 apertures have the large and small offset so that the POI changes when flipping between the two.  (Supposedly for 300m on the small and 200m on the large.)  The 40L retains that, while the 40L SP has the two on the same plane so the POI doesn't change when switching back and forth. IMHO the same-plane is the better option because you're going to be using a BUIS at close range and not adjusting for distance.  Just set it for the 50y/200m IBSZ and hold COM at anything out to 250yds.  Use the two sizes to adjust for speed/precision or lighting conditions.

I don't think a standard A2 sight shows a POI change between the two appatures.  For shots past 300m you would need to dial in Elev clicks on the drum.  Just switching to the small peep does not raise POI.

If I am correct then the #40 SP would mimic this behavior.  However since the #40's don't have any elev adjustment the #40L would allow you to get a little more Elev out of the small apputure.

BTW both the #40L and the #40SP have the same overall dimensioins.....

Quoted: The A2 apertures have the large and small offset so that the POI changes when flipping between the two.  (Supposedly for 300m on the small and 200m on the large.)  The 40L retains that, while the 40L SP has the two on the same plane so the POI doesn't change when switching back and forth.

I was just rereading your post..  are you speaking specificly of the ARMS #40A2 sight?  Or the standard Mil A2 sight?

The standard .mil A2 sights are supposed to be set for a 300m zero with the dial at "3" with the small aperture and a have a 200m zero when flipped to the larger aperture.  I believe the #40A2 uses the standard .mil A2 aperture so it would have the same offset.  The #40L uses a different aperture configuration, but apparently they kept the offset between the apertures, except on the SP model.  

The 300m zero puts mid-range too high for most uses so the IBSZ procedure adjusts the dial to let you use a 200m zero with the small aperture.  If you flip to the big you adjust the dial.  Since the #40 doesn't have the dial you either have a shift in POI when you flip or you get the SP version.  Depending on what ranges you think you'll shoot at maybe you want the offset.  I would want the SP.

Hijack:

Does anyone sell same-plane apertures that have apertures the same size as the A2's?

The only same-plane for regular sights I know of is the XS one, and that has larger than A2 apertures.  I don't know what sizes are on the #40L-SP or Troy BUIS; the #40L-SP might be A2 sizes, Troy I suspect is larger.