Just installed High Sierra on my 2010 mac pro. Technically a 2009 4,1 with a firmware upgrade to 5,1 and a new processor. I can load it if I remove almost all of the peripherals. ...This is the error message I got when I finally got it to boot up:
...
Kernel Extensions in backtrace:
com.SiliconImage.driver.Si3132(1.2.5)[9A111ADF-FA93-E94E-5440-5BE653899A6F]@0xf fffff7f8e2e0000->0