I'm not surprised by the finding that a good 8x43 can put the mighty 8x32 SE to the test.
I was actually rather let down in a couple instances with the 8x32 (it isn't perfect, after all). I was out on a boat and birding in horrid light. Despite all the "eye pupil this" and "exit pupil that", I have the suspicion that a 5mm exit pupil is also useful in harsh light. Anyone have any thoughts on this? Say you have mid-day light, you have a back-lit subject. Does it stand to reason that a "brighter" binocular will have better performance on the poorly lit subjects? Or maybe that's when you want more magnification to compensate?
A larger exit pupil for poorly lit subjects, yes, back-lit subjects, no, since your entrance pupils will contract to the same size looking at a brightly lit background in either bin.
Here's a couple ways to eek out more detail from your SE in a back-lit situation. Pull your eyes back from the EPs until only the bird fills up the view.
Your entrance pupils will open up more and you will see more detail on the bird, because in bright light, your eyes switch from the rod system to the cone system, better for color but not as light sensitive.
You might also try using averted vision to eek out even more detail after you've backed off from the EPs and reduced the background light.
Instead of looking right at the bird with your central vision, look just off-center so your peripheral vision, where most of your rods are, picks up the bird.
This technique is used in amateur astronomy with dim celestial objects, but I've tried it for birding, and it also works in this situation.
However, it's hard to master this techique if you're not used to it, because your brain keeps drawing your eyes back to the bird and your eyes are constantly scanning the image.
Try this indoors. Stare at a thumb tack at the top of a picture of photo on your wall or put a push pin in the wall and concentrate on it.
Try not to move your eyes (it's harder than you would think). If you can do this, you will notice that in a while, the picture or area below the pin will start to "disappear".
Yes, it's good to have a full sized bin to back up your midsized bin on overcast days and in the winter.
I mentioned on another thread that I sometimes find the 8x32 SE lacking when light levels dip low on completely overcast days or during the winter.