This reply from Himni Racing in Fla about an oil restrictor for the Garett GT30 turbo:
"... the turbo should be used with water. Not doing so will drastically decrease it's life. Without water, the turbo has 12-14 months life span. With water, countless years of performance will be had. Not using water will also void it's warranty. If you don't use water, you should drill the oil fitting out to a .070 size. (Twice the size of the hole that's in it now). Careful not to go too much as it will cause issues too."
hmmm.. what do you all think? I haven't heard of anyone using water cooling on a bike with a turbo yet...