Revisit potential use of string.utf8 field for conversion to data

[carlbrown]

See PR #20 for history.

Need to revisit this after #96 is complete and we have a perf baseline.

[helje5]

Not that #96 is not based around Data but DispatchData. That may require a completely different 'best way' to do it. (I think I do it in a very inefficient way in #96 and convert String to Data, then Data to DispatchData 🙄 - but that should be fixed)