Hi Jeff,
This was part of my college degree final project and the focus was on adding functionality over the string search with a new FIND function and creating an easy, standard, intuitive and readable way of operating transformations over a string with a new STRING function.
Both needs that I think urge on SQL Server and come in the way Microsoft has been building on the most recent SQL Server versions.
Therefore, the performance was not the focus but anyway analyzed for several examples in comparison with the current alternative using the string SQL system functions and the results were, as expected, poor, mostly when executing the STRING transformations with multiple operator.
Here is the complete report on the assignment.

Best regards
Pedro Costa