Many thanks to BrowserUk for the excellent reply and apologies for the delay in responding. I have taken all these changes and incorporated them into my script. Are there any sources of information where these techniques are described? A cookbook for fast code if you will.

On attempting to measure the performance improvement, I discovered that the profile I posted above was in error. dws was absolutely correct in that another part of the code was in large part responsible for the slow execution. That being said, the version of GetMininalDataType that BrowserUk created ran against my test data in approximately 60% of the time of my inferior version.

Regards,
Dom.