Just updated to 2.0 and the new main menu aswell as the sin menu completely tank performance. FPS are in the low 30s when it was around 100 before. Once in game performance normalizes, unless the aspect unlock menu is opened, in which case performance abruptly degrades again until it is closed.
According to the taskmanager, the "GPU Copy" raises sharply towards the 80% mark while either of the offending menus are opened and returns back to zero as soon as they're closed.
Radeon R9 390X (current driver, fresh install)
Edit: Normal pause menu while in game behaves normally.
Edit 2: Here's the output_log.txt
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