I just recently got my TDI going, about 300 miles on it so far and I'm presently burning 40% D2 & 60% W85 (WMO) and since it likes that fuel fine in a day or two I think I will go to 80%.
Be carefull with running bio fuels thru VW motor. They have huge kocking(sp) issues unless the fuel lines that run from the IP to the injectors them selfs are insulated and heated.
FYI.
Also for you guys running TDI. Delete the EGR and clean the intakes. Makes a huge difference on how the car drives.