Wow over 40mpg sounds very nice!
My best tank so far in the 300DT was 34, might have been shortly after switching to summer fuel but was probably on winter. I was getting ~32 on a half dozen tanks with winter fuel before but it has been going down lately.
Anyway that looks like a very nice MB there, I prefer turboed but then again I'm BOOSTNbenz. My last three cars have had turbochargers.