Here are my honest thoughts on your post, Birdman---
You are on the right track in patterning different loads in your shotgun, they do NOT always pattern the same as barrel markings.
I assume you are running into some late season savvy birds that are running/flushing wild on you. I don't know if you are hunting with a dog, or if so, how experienced he/she is in finding cripples. A guy once told me, rightly, that a shotgun is a short range shooter. He is right. Another thing to think about is, what is the nature of the shots you get at 35-50 yards? For example, are they straight away shots with you shooting at the bird's tail? Are they right angle or overhead shots so that the vitals and/or wings are exposed?
Speaking ONLY for myself, if I had a crossing shot at 40-50 yards and I could drop the bird in light grass or a plowed field, I might take the shot IF my dog was nearby, following the action. I would not take the shot if the dog didn't see the flush, or if it was a straightaway, or if the bird, if hit and possibly just winged, would fall into heavy grass or cattails where retrieval would be problematic. I just feel too badly if I hit one and can't recover it. So I guess my thoughts are, it depends on the circumstances. Certainly the MOD/FULL chokes and #5 shot would be a responsible long range load---depending on the above and other factors....like how tired you are, how is the light, etc.