Storing data in Oracle or .mat files

We are trying to do some post processing on a large amount of data from Oracle and then produce a report at the end on a regular basis. I was wondering, would it be more efficient/quicker to store the data in a .mat file (going to be up to 1,000,000 cells in each mat file) which MATLAB will have to hand to perform calcs etc or saving the changes to apply in a mat file then import the data from Oracle into MATLAB each time?

Thanks