ns_cache names is 76000 microsecond with 500,000 cache entries and a simple match like "XYZ*"
util_memoize_flush_regexp is 1600000 microseconds with 500,000 cache entries and a simple regexp like "XYZ.*"
So ns_cache names is about 20x faster. There isn't anyplace in the toolkit that a regexp is required and simple match would not work.