My engineering opinion is that going with the 3/8 thickness will be just fine. It's 96% of the thickness of the original, and it is not like 3/8" material was available in France and rejected because it was too weak...
It is unlikely that the darker color will significantly affect the crazing that occurs with long term UV exposure, since that is predominantly a surface effect. I am not a fan of the tinted windows, but that is really just my own esthetic, not an engineering judgement.
Choice of material for this application is always a trade-off. Lexan (and similar brands) are stronger to impast failure, but shorter lived in UV exposure without custom coating. Here is a good summary:
I am not sure what the original material was on the windscreen. The panels on my boat were replaced with 3/8" clear plexiglass by the previous owner.