I agree completely. My oil pressure also increased from 0.5 bar to 1.5 bar once the switch to Mobil 1 15W50. My idle speed is also around 500 rpm when warmed up.
I HIGHLY recommend synthetic oil (of the proper viscosity) in the M119 engine. You want to give the valve train, including timing chain, every advantage. A valve job in an M119 engine runs about $6000! Also, these engines tend to run a bit hot, esp. in a W124 body.