I put an old PowerShell Excel script out on google docs that I put together for a user group presentation about 2 years ago. I use it for a few scheduled reports. I wouldn't write it now the way I did then, but hopefully it will still be useful. I am not sure
how these port to EPPlus. I thought, perhaps, it may give some ideas.
If you don't implement some of what I use, I'll eventually get around to it and send it along. I may also revisit for a future user group meeting.
Some of the other things I have done with Excel I have had large speed increases by generating CSV or HTML output and using the Excel import features to do the cell by cell work (Join-CSV). Again, I don't even know if it is applicable or even needed with EPPlus.
Let me know if the link doesn't work or if you have questions.