Well, I just checked, and it is written in the Omegamania Book that the Railmasters were resistant to ... 1000 Gauss, exactly like the Rolex 1019, when the former crowned Milgauss was " just " resistant to 800 Gauss.
The JLC Geophysic is resistant to 600 Gauss ( not the Deluxe ).
And about Patek, my guess is that it is around 500 Gauss, but not sure at all...
Best, my friend.
Will post soon, in one or two weeks.
Nicolas.