I came across your post while searching for a identical problem I have with my new pc system and a threadripper 1950x, I don't use premiere but edius and have exactly the same problem as you do, a lot slower program load and a generally more "laggy" feeling while using the program. My older i7 4790K also loads edius a lot faster and feels faster while using it. Performance while rendering/exporting a film looks good though, it's just the load times and the general feel while using the system, it's like it needs to think a bit before it acts.
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