You also gotta look at the fact that a diesel engine normally has a compression ratio anywhere around 18.0:1 so running it at 10.0:1 is regarded as a decompressed engine, If you were to halve the C/R on a gze I'm pretty sure you could run around the 40psi mark safely (Backyarder runs 30psi reduced from 40psi in his 4AGTE 20v and runs 10's), And i doubt that you would be able to push much more from VW, Have you ever driven a turbo diesel, The new nissan navara has a 100kw diesel yeah it might be heavy but at the end of the day a diesel uses forced induction to aid it through the rpm range, I'm yet to see a full-on performance car based with a diesel.
EDIT:
Ha just realised the VW GT is A Petrol :jamie: