DO NOT flash to the latest 3.4.1 BIOS as it will probably brick your system.
I found this out the hard way.
The new 3.4.1 BIOS and other system firmware updates ISO was released 06-12-2018 and available on the DELL site so I downloaded it and burned the ISO onto a DVD and then booted from it. Updates were going smoothly when all of a sudden the monitor screen went blank. I waited for hours but all I had was a blank screen. I forcibly had to power off. When I then powered-on the fans spun up and down but no BIOS screen was ever seen either on the built in VGA port or on the GTX 750 discrete card. The front display status (when holding right button for 5 seconds) states "No Post Code".
The R815 in question had quad Opteron 6238 Engineering Samples (ZS262445TCG45) in it. It was working great on the 3.2.2 BIOS but had older other firmware in it which was my main reason for updating it. The 3.4.1 Bios Update is a Microcode Update (probably for Meltdown/Spector) and I am not sure if having the Engineering Samples in it was why it got bricked.
Needless to say I am not updating any of my other R815's.
FYI: The R815's with quad Opteron 6238 Engineering Samples hash at 1700 H/s. I have three R815 systems with them and two other R815's with quad Opteron 6234's that produce 1570 H/s. In each of these systems I have added a single GTX 750 which adds 230-240 H/s.