After 4 months, I now believe that I have solved my BSOD 0xf4 problem. I was searching around on the Microsoft support web site, where I ran across KB977178, where it describes Windows 7 machines that might give that BSOD code when waking from Sleep, and having a large SATA drive.
http://support.microsoft.com/kb/977178My C:\ drive is a Samsung 840 Pro 256 GB SSD, but I also had two WD1002FAEX 1TB HDDs in the system. I started checking all three for any abnormal signs. chkdsk never found any problems, and sfc /scannow always ran clean. When I installed PassMark's Performance Test PC Benchmarking software, and went into the Options to change which drive it would test, one of my two 1TB WD HDDs was only getting about 60% of the bandwidth that the other identical drive was reporting.
Since I had already tried everything else, I ordered a newer WD1003FZEX for US$90. This newer version was even much faster than either of the WD1002FAEX drives, and I have not seen another BSOD 0xf4 in the 3 weeks since I changed that slower drive out.
I can only speculate as to why a slow, non-boot HDD would occasionally cause a BSOD 0xf4 when doing things like turning off a printer, inserting or removing a USB flash drive. The only thing that I can think is that the Z87 was too busy retrying, or otherwise dealing with a problematic drive to allow it to service the other I/O functions that it controls in a timely fashion. That is speculation on my part, but I now feel confident that I no longer have that very frustrating problem with my computer.