I would be really interested to hear your thoughts on the Cumulate function and how you have best utilised this without affecting performance? I understand on longer time ranges it is usually, but not always, beneficial to use Previous instead of Cumulate however would you also break the function out in several line items or complete the entire operation in a single line item i.e.
1 Line item with Formula = Cumulate( X[SUM:Y] )
Or Line item 1 = X[Sum:Y]
Line item 2 = Cumulate(Line item 1)
I would definetely split the line items, to make use of multi threading.