It's not only the higher octane rating of LPG that makes it an ideal fuel for turbo motors, there is also the cooling effect. Where this can cause a problem with icing on NA engines, it hust helps to cool the charge on a boosted motor.
Also you are exempt from ADR pollution controls - you only need to comply to your state's LPG conversion requirements (normally need to have a gas fitter's lic. or similar).
There was an old Valiant with a turbo Hemi six running LPG in a magazine a few years ago - a street car, not drag machine. Made so much torque it started to crack the A pillars
I believe that ALL the aussie car makers will be producing dedicated LPG vehicles this year, using liquid phase technology. Engines will all produce more power than the ULP versions, and use 10% less gas than vapour phase regulated LPG. It's only dual fuel conversions that suck.
Check up on Clayton (Fez). He and his mates are working on something like this for a Mini...