Gonads

Correct me if I'm wrong, but a water cooled turbo should still have water flowing through the core after the car is shut off due to convection. The convection will stop when the core temp drops back to something similar to the block. You should not get any coking on the bearing surfaces with a water cooled turbo even if you thrash it right to the pit garage. Having said that I tend to take it easy for the last bit of the trip.