I tested every possible setting. SSAA and MSAA on and off. With MSAA off, average FPS is higher, but FPS dip still exists.
I uninstalled LED applications, yet there is not difference.
I agree with you. This kind of performance with 50% resolution is ridiculous. I remember about 2 months ago running full SSAA and MSAA with 80% SteamVR resolution with ease.