I tried putting the squats at the end of my routine last session and it was a major FAIL. I 'may have had a little more strength at the beginning, but I was wiped out by the time i got to the squats. I couldnt lift what i wanted to and weight and reps suffered for it. My legs were shaking just doing my second set of squats at 100kg when normally working weight is about 130kg !!! Although i was alittle short on time and i may have taken lest rest than normal, but it still didnt feel 'right'
If I do squats first when freshest (well second after an oly lift) then i can hit more. i may fatigue quicker as i get towards the end of the upper body stuff, but if BB Curls are sub-par Im not really as concerned as if squats are.
I have done Deadlifts at the end of a 'back day' on a split which seemed OK. i couldnt lift as much but they were a good finisher, but for the fullbody I prefer to work through from (in most cases) heaviest to lightest.