I don't have a turbo on my Subaru, but my dodge truck has one - its a Cummins 5.9 lt. diesel. My exhaust gas temperatures (I have a temperature guage with the probe post turbo) are running in the 450 degree F range when I pull up to park (this is without a load). I let it cool down to 325 degree F before shutting it down, takes about a minute and a half idleing. Since oil will cook a little higher than that, it saves the bearings in the turbo. I beleive that a gasoline engine runs hotter than a diesel, than everytime you shut down hot, you are cutting the life of your turbo. This is my opinion.