Recently picked up a 1div and have used it at two race meets now.
I usually use my 5d3 and 70-200f2.8ii and are happy with most of its shots
As the 1div is new to me, I am loathed to use the 70-200f2.8 on it yet as I am still very much learning, and dont want to end up with mainly bad shots so I have tried : -
100-400, and not been very impressed
70-200f4 + 1.4 extenderiii - reasonably impressed
70-200f4 better still
is this as to be expected??