How many people have upgraded the S4 firmware to: initramfs.bin.SD-20141016.tar.gz from the bitmain website?
I only ask because mine is still running on the factory firmware no problem with difficulty manually set, so I'm kind of wondering if I should bother with the upgrade.
I don't think you'll be able to get an accurate number of people

Even if you don't currently have any problems you might have issues if you ever want to switch pools. I had trouble with some rentals - for some reason even December delivery S4s came with old firmware - upgraded to the 1016 version and haven't seen any problems since.