OK another update. My previous tests were all with blend which is how I left it from previous testing. With duplicate frames 8% works better with Spidey and as well as 6% does with dumb algo. None of them are great but I think this is an issue with the model. From previous testing a few months back, setting SC at below 6% with the dumb algo will fix this issue while causing stuttering everywhere else. It's almost as if it turns of SC for that scene.
I hope some of this helps. 8% with nvof and duplicate frames might end up being my default from now on. But then I can find at least one other scene where the best option is SC=100 and the square is solid blue so...?