The ISO500 lock isn't about lowest noise, it is aiming to give you the best balance between dynamic range and noise, so it accepts a little more noise in the shadows to give you more range overall.
Just a suggestion, but it might help to get a response if you were more specific about what you need, airframe only, which camera, or no camera required, batteries, ProRes/Cinema DNG license etc.
Hope you find what you need though...