About the only way to get reliable comparisons is via an online league that does hash checks on the pertinent files.
And this thread reminds me of a couple of things I've long decried in GTR2 - you cannot export your player records, nor can you individually delete any (ages ago I installed a Caterham mod, very nice but performance was TOO good, I removed it after a few months; but to this day my track records are haunted by this car ...faster than F1 cars, faster than LMP cars, faster than Group C cars).