I tend to scale the envsphere up to 1000%... out of habit really a lot of the time. I'm not sure there's necessarily always a benefit in doing this?

Well, as I'm finding in a scene I'm working on at the moment, using one of these Vue panoramas I've made, I'm realising it does affect the position of the horizon line, potentially;

i.e. in the current scene if I make the envsphere 100% scale, the horizon line is hidden behind the wall of the Car Patio set.

If I make it 1000%, I can see the horizon... and therefore some of the ocean.

In terms of camera YON, I've previously found some weirdness, rendering, when trying to scale up really, really big... much above 5000% scale for envsphere, I think... see the linked thread:

http://www.renderosity.com/mod/forumpro/showthread.php?message_id=3902706&ebot_calc_page#message_3902706

(my understanding of Poser measurement units was a bit flawed at the start of that thread by the way - and I think I've subsequently changed to measuring in inches)