I have driven several FIA GT 2003-05 championship seasons and achieved very good mixed up results with the following cars:
rss_gt_vortex_v10
rss_gt_ferruccio_55
rss_gt_ferruccio_57
rss_gt_lanzo_v12
rss_gt_tornado_v12
rss_gt_shadow_v8
+
rss_gt_adonis_d9_v12
+
tmw_porsche_carrera_gtr
legion_corvette_c5r
ks_maserati_mc12_gt1_2010
Download the readme, you`ll find ballast and restrictor settings for the cars above there for V. 0.75
Note: I wouldn`t drive the Corvette as she is much easier to drive than the rest of the cars. But she works perfectly as AI car together with the grid.
IMPORTANT: The results will vary from one track to another. Depending on track characteristics.
Tested on all official FIA GT 2003-2005 tracks.
Any feedback is welcome. Have Fun!