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Maintain Aspect Ratio or Scaling settings will remain even if you restart the computer. This feature is called mode persistence.
I recommend testing new drivers on your computer.
Driver version: 184.108.40.20637
I've tested mentioned driver (it shows version 220.127.116.1137 on the info screen now), but haven't noticed any differences. There is still no such an option as "keep proportions" when already at 16:9.
Please bear in mind that our drivers are generic and not all features may be available for your computer model.
I would say you need customized drivers from your motherboard or computer manufacturer as they are familiar with total configuration of your system.