Just to update, I've gone down the powershell route. The files I'm working with are actually XML files, but I need to read them in as text, Workbook.OpenText doesn't like that, and just tries to load the file as XML. So the faff of having to rename the file to .txt, load in as text, then get the text into memory from the worksheet and use Join() to decipher the XML was too long winded. Using powershell you can use the [io.file]::ReadAsText command, and then WriteAsText to output as ASCII, this is pretty much instant (with ~20MB files anyway), and then I just have to load this file in as normal. As this process has almost no overhead it's the obvious choice for me.