It might be useful to know that every call to Calculate will reset the values on the worksheet. Therefore this:
mySheet.Cells["A1:B2"].Calculate();
...will be faster than this:
mySheet.Cells["A1"].Calculate();
mySheet.Cells["A2"].Calculate();
mySheet.Cells["B1"].Calculate();
mySheet.Cells["B2"].Calculate();
The formula parser will start by building a calc chain and calculate the formulas in the appropriate order, so you don't need to think about that.
How many formulas do you have in your worksheet?
