Can you supply more detail about what you are trying to do?
I think the biggest factor is going to be the amount of data that will be used to generate the .xls(x) file. You can't fit 10 lbs. of content in a 5 lb. bucket.
I'm trying to have the print preview in excel sized automatically in lieu of manually clicking to fit all columns on one page.
I would like to adjust the margins as well to accomodate more real estate.