This is how I have "fixed" the brutal fps loss from SU11

User Support Hub Install, Performance & Graphics
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  1. NVIDIA RTX card user: If you undervolt your card, you may have gone too low, even it may seem fine in other games.

  2. Road, boat and shipping traffic causes stutters and low fps at any setting, so I’ve turned it off.

Changing these two points makes my sim GPU limited and smooth now, with very rare hiccups.