Effective resolution of viewport exports?

When you render to extra viewports ("viewport exports"), will it render to the resolution that is configured in DCS "Resolution of Cockpit Displays", or do you get some random aircraft device-specific resolution that is then stretched to the output viewport?

Or does it actually render natively to the viewport size that is specified in the monitor setup without subsequent stretching?

In another way of thinking: if you wanted to decide what size to make MFD exports for good visual quality, what size would you make them? Pretend you have whatever display size available that fits, so don't worry about that.

Understanding this precisely has major impact on viewport export tech I am working on for Helios. It would be nice if someone has already done this research, so I don't have to do 1000 tests :)