Thanks guys. I thought there was a possibility that the latter kit was just a re-box with an added sprue to bring it up to E standards, but sounds like this is isn't so.
Clay, it's okay as it looks I'll be going to ebay. Squadron store is showing the StuG. III Ausf E as being out of stock, and atm Spruebrothers is only listing specific kits available for Black Friday sale.
regards,
Jack