Hi Bryan,
Return value only supports integers, as it needs to match the value to a return code. We are considering a range of enhancements to this functionality, and I will note your request in our backlog.
In the meantime, my recommendation would be to write a python script to perform this comparison and get it to return an integer value (example exit(3)) that you've configured on a subsequent step path. Like what you would do for return value.
Run your python script using the 'Executable' step type.
If you have any other questions please let me know.
Cheers,
Michael