Wow. My Cummins ISX and Detroit 60, along with previous N-14 never gave any kind of warning even when EGT's got to 1100F. My Detroit 60 with a Borg Warner 171702 turbo gets 900F frequently on hard pulls on a hot day. Sometimes 1000F if I am not watching things as closely as I should and wait to drop a gear and get the RPM's back up a little. Put 1.4 million miles on the N-14, still had original turbo and it only got Kendall 15w40 conventional. Same for the ISX, but I sold it at 983,000 miles. The Detroit now has 540,000 miles on it and nary an issue, but it is getting a Schaeffer syn blend 10w30. Those are some low EGT's, Doug. I only see those "normal" temps when I am putting less than 10 lb of boost with a light load. Only the VG turbo on the ISX was water cooled. The BW 171702 I am using on the Detroit 60 isn't, nor the Holset on the N-14.
Lots of fleets using conventional 15w40 with their less than stellar company drivers who could give a rip about EGT's (many company trucks don't even have pyrometer gauges) and there is not a line of broke down trucks down the highways.
Not sure where the idea that oil temps were getting anywhere near the EGT temps came from. There is a high volume of oil being fed thru the turbo that there is no way the oil is getting that hot. Even at 900F EGT's on a hard pull, my oil never exceeds the engine coolant temp.