Thank you, Richard for adding the comment below and pointing me to the La Parola Greek Testament with both variant readings and a list of Patristic citations. It is both magnificent, and a fine example of how (if the data are in suitable formats) people online can build on, and add value to, each other's work. You have put together a really useful site!

Richard lists het following resources which have been used in his project:

• James Tauber and CCAT (Center for Computer Analysis of Texts) at the University of Pennsylvania for the Greek Text (Nestle-Aland and the UBS, and is only available for NON-COMMERCIAL personal/scholarly and educational use.) He notes that he "added the punctuation to the text, and know that it still contains many errors" so do your bit and write to the address on his site if you find one.
• Christian Classics Ethereal Library for the Westcott and Hort text and Maurice A. Robinson for the parsing and for the Byzantine Text.
• Ulrik Petersen for the Tischendorf text.
  
  
• Christian Classics Ethereal Library for the text (in the Ante-Nicene Fathers translation) and Early Christian Writings (Peter Kirby whose blog seems currently unavailable) for the index to the fathers.