This is my one paragraph essay for question 5. It took about four minutes to write, then another minute to edit it down to under 120 words (to be precise, 119). It was scored 5.0.
So essay 4 was 107 words and got 4.0. And essay 5 was 119 and got 5.0. I'll write the next one in 110 and see what happens.
This also suggests that ETS isn't necessarily looking for multiple paragraph essays.