First of all, thank you so much for taking the time to test the scene, Rutra!

Quote - I couldn't render it in Vue6, for comparison, because the scene was saved in Vue7.

DUH! I should have sent you the Vue 6 version... :O

Quote - ...I disabled the clouds and it rendered in 5 seconds...

Hmmm... maybe this is worthy of a bug report, then...? Because it seems odd that Vue 6 should be able to handle those clouds beautifully & quickly, but Vue 7 drags terribly when using the same exact clouds.  

In short, I thought Vue 7 would be able to not only match Vue 6, but excel it...
I appreciate all your help! At least I now know what the problem is. :P