Hi SmallFry,
I had Sky Light enabled, Indirect Light enabled and set up for Ambient Occlusion only, a couple of Anything Glows lights, and Caustics. All this on a WinXP PC that’s about 5 years old. It’s a scene filled with ice slides, a Stonemason building set, about 6 LoRez figures, 2 Mike3 figures with clothing, and a partridge in a pear tree.
Well, that ‘splains it! It was the %$#&! partridge! 
I hope you had use of another computer during the render(?)......if not, Do Not Pass Go! Go directly to Frys, Best Buy or NewEgg and
get the cheapest computer if necessary to be your render box…..it will no doubt be way better than any 5yr old.
You will live longer due to less stress, have your cake and eat it, too.
I have a 5yr old HP6226 laptop that still works great, and was the cheapest I could find at the time ($700) to replace a $1900 computer
that was being worked on in the shop.
I’m amazed at how much computer you can buy today for $350! ......they’re almost disposable….people pay more for smart phones!
Life is too short for 4day renders, imho. 