I'm using standard 6.5 cm separation values in both external and internal views. This is because it corresponds to typical human head being placed inside the game world, and this makes it quite realistic in that aspect. Smaller values would mean unrealistically small depth differences, while larger values would exaggerate the depth differences which I personally don't want in a game. Whether the image is scaled up or down in apparent size doesn't really change that fact, and this separation value also enables me to utilize German and certain other gun sights the way they were meant to be used.
I'm also using 2 degrees of convergence so that distant objects are separated on the screen, making them appear to be further.
I am aware that a lot of things also affect the perceived distance of objects, but I also prefer to show the images as I see them when using the mod. I don't know if there can be any "preferred" mode that could be universally superior, so I'm just showing what I'm seeing, and personally I like these settings.

It does take a bit of getting used to, and since convergence does not adjust when field of view is changed, large changes in zoom can be a bit jarring, but it's all pretty manageable after a bit of acclimatization. Or maybe I just have exceptionally versatile stereo perception, I dunno.
Also, I made the images into links to the original, so you can view them bigger simply by clicking them. I just used img width=960 tag to downscale them on the forum so that they don't disrupt the forum layout...