In expert mode, you G27 will work as a real wheel on console.
In legacy mode, you G27 will work as a controller on consol, as other converters generally do.
So there is a big difference.
If you like to try G27 on FH2, you should choose FORZA5 's config.
But it will only work in legacy mode.
As for Forza 6, we are still working on it, you may wait for the update.