S!

How about 6DOF + if using snap views you can save head positions. This is used in Aces High online WW2 combat sim. Simple and works.

In Il2 I have my gun sight and normal views mapped to one of the hats on my Joystick. When I'm in a situation where I need to use the gun sight i'm fairly well concentrating on the target any way so I not really paying attention to much else so the situational awareness isn't much of an issue for me.

If there's tracers wizzing passed my cockpit then it's my team mates shoulder shooting or an extremely bad shot! ;) Either way it's time to go back to normal view and assess the situation!

Same here. Simplest solution, IMHO, as it takes only a millisecond to switch between steady aiming and checking six.

I will not argue whether it is an optical illusion or not but when I lose a good 10% or more of my viewing area I will say I have lost a great deal of SA.
If your theory holds true then looking backwards I should have an increased FOV. Test that out and you will then discover be it a head movement forward as you claim or an optical illusion your FOV is restricted in any direction you choose to look from normal view...
Put your self in a bomber pilot seat and you will inderstand.
Use Shift + F1 and you will suddenly find your view restricted no matter which direction you look.

Sure, but that's how it is in reality as well, If you're looking down the sights of a gun your view IS limited compared to just loosely look in the direction your gun is roughly pointing.

I loaded up IL-2 again and carefully went through the following aircraft:

B-24
B-17
H-111
Fw-190A8
Bf-109E4
Ju-88A4
AC-20

The heavy and medium bombers (except Ju-88 and AC-20) did not have any kind of gunsight and in most of them, Shift-F1 moved the view between pilot and co-pilot seats.

Looking forwards as well as backwards, it is as expected: it moves the head into a new position (usually forward the most in every plane. Movement to the side occured in some of them (in He-111, it moved forward-left even). In the Fw-190, the view also moved upwards a bit.

Looking backwards in all the aircraft while switching views - both over left shoulder, and right shoulder, one can see better and more in gunsight mode as the seat/armor plate is further away. In the 190 one can see the elevators on the right side even which are otherwise hidden. In the Ju-88 one can see much more everywhere, mainly because curtains are present behind the pilot up to about as far as his seat support so any movement forward gives better views.

There are a few planes where the non gunsight mode is extremely much higher (in a cheaty, unrealistic amount). The Me-262 is maybe the most extreme. The Me-210 and 410 (if you have them) are other examples. Using gunsight in those planes very much gimps the view in any direction, but on the other hand, that is still the most realistic view for those planes (one does not stand in a cockpit in reality.. :-P ).

In the aircraft where the gunsight is offset to the right, looking back over left shoulder did not give much (if any) different view because the head was offset to the right, cancelling out the forward movement.

You can try this for yourself. Try also to look straight down, or straight sideways while pressing Shift-F1 to see how far forward and back the move is.

Never the less, the move forward does bring the canopy pillars closer, and makes them larger, and this gimps the view to an area to the front in some planes (Fw 190 a very big offender. Same thing happens in spitfires if one leans forward). I know I never liked flying in gunsight view because of the pillars etc being closer, for pretty much the same reasons you have now. After switching to head tracking it was no longer an issue but I still remember...

maybe.

Agree that being able to choose the 'center' for the head would be a good feature. In any plane without center gunsights, I keep having problems with the centering. It can be ok to be offset, but often is too high or low when I try to lean into gunsight.

This is great news, SpeedTree do a wonderful job.

Which version οφ σπεεδτρεε Σιρ ?