If I'm understanding how you're doing this, you're choosing between medium and large sizes of the Flickr bb codes? I've also noticed my photos being softer on here. But how are you getting your 3 photos all to look the same size?
If I post a photo at 800 and at 1600, the 1600 looks too big on here.
As far as what I want to shoot with the smaller focal range lenses, I guess landscape and street, and there might be times I want to shoot in low light, kind of like those evening photos of the pub a few pages back which were shot on an a7 lll. But since you're saying
aps-c up to ISO 6400 is fine, that gives me more confidence in an f2.8 lens.
Well FF would be better and I'd love an a7 lll but there's three things stopping me. On aps-c, I prefer the 1.5x increased focal range on the 70-350 telephoto lens, it's not big and heavy like a 150-600 lens, and it has real time tracking.