Sorry to respond over a week after the last post, but was searching for threads on performance after just completing a patch 6 playthrough (hadn’t played since patch 4).
Performance in game was fine, but loading times were ridiculous … minutes to load a save. Then I tried using DirectX 11 rather than Vulkan after finding an old reddit thread saying it could help load times, which it didn’t AND made performance in game absolutely terrible. So while this probably is not the problem the OP has, thought I’d call out that I am getting appalling performance with DirectX 11 (with an RTX 2060 card) but fine with Vulkan.
And if anyone has spotted a more recent discussion of long load times and could point me at it that would be much appreciated. I have an SSD so that shouldn’t be the problem.