I could be wrong, but the Create Audio 5AR4 looks like a relabeled Shuguang.
Whart, "I haven't tried any tubes that are currently manufactured, apart from the Chinese tube mentioned above."
If it's the standard Shuguang 5AR4, the Mullard provides a good step up in sonics. The JJ also will, and in most of the applications I've tried, sounds almost as good as the Mullard. Unfortunately, the Shuguang has proven much more rugged in comparison to. The JJ tend to arc over at conditions the Mullard and Shuguang do not.