String operations will always be faster than regular expression operations. Unless, of course, you write the string operations in an inefficient way.
Regular expressions have to be parsed, and code generated to perform the operation using string operations. At best, the regular expression operation can do what's optimal to do the string manipulations.
Regular expressions are not used because they can do anything faster than plain string operations, it's used because it can do very complicated operations with little code, with reasonably small overhead.
