The best way to get that off is to use a clay bar, not a polish. A clay bar will take all of the transferred paint off very easily without abrading your paint. You'll be left with some marks from the accident that need buffing up, but you shouldn't need to be using anything as aggressive as G3.
Sorry but clay bar isn't the right thing to use for that. It *might* remove some of it, but I would not use clay for transfer as heavy as that, its far more likely to cause a problem than it is to solve one in that scenario.
And I'm not sure what you mean that G3 is too aggressive. G3 is a range, not a product, so if you pick the right product from the range then it will be spot on.
I would use G3 ultra on the flat areas and G3 fine on the edges, and a machine polish of G3 finish over the lot to remove any fine marks when all the colour/transfer had been removed.
If you really want to cheat, brake cleaner would remove it. But it's a "cheat" and if you are unlucky, It can make the too coat to milky, which would then require machine polishing anyway. So it's best to do it right first time in my view.