Thanks guys, it just seems so odd to me that something that was completely built and working in GT5 (admittedly as DLC.. which was odd) would just be cut out entirely.
While it's a shame that the game struggles to match real life from performance to data (hello obese lister storm and mclaren f1 gearbox) comparing performance within the game is still valid. But without any testing abilities a lot of tuning remains guesswork, a lot of my tunes were done in order to match cars to there real life variants much more closely.