Ok, you had to know it was going to be mentioned eventually
but I would feel pretty comfortable doing that job with a mulcher on a skid.
Granted, while a mulcher is a specialty machine and is relatively hard to rent (at least in my area), a mulcher should be able to handle your project in less than a week using one machine with one operator.
Did I mention I travel?
BTW- I'd rather leave the 5-8" trees standing and mulch them in place. It would give you cleaner results and would be faster.