Thank you !
This has been identified as an issue with Low Quality scope details paired with SuperSampling. Unfortunately the fix did not make it into the hotfix update released yesterday.
In the meantime, you may simply switch SuperSampling off or play with High scope quality settings.
Same issue for me. low scope detail + 1.25x supersampling are the settings I am using. This is ideal for me. the fps drop in high detail is significant and FXAA looks terrible in all games. im glad 1.25 SSAA is available. I get really solid fps now while using high powered scopes which is awesome thanks guys. I'm perfectly happy playing with ironsights and red dots for now though. I'll try out TXAA now that its been implemented.