I’ve tried 1 and 3 and performance hasn’t improved. I really like my theme, so wouldn’t want to switch from it even if it is the problem.
As for point four, I am not really sure how to do that.
Is there an easy way to uninstall 3.5? Judging by other posts on the forum, it seems as if this release has a lot of issues. I think it would best to rollback, however, all of the guides online involve very technical processes.