Paper's about 0.1mm thick. Therefore 513km of paper contains approximately 5.13 billion sheets.

Given that there's 11TB of data, that means that each sheet contains about 2360 bytes. (Printing on one side.) That's an 80x30 grid. A4 is 210x297mm, so (holding the paper landscape for convenience and assuming a 2cm margin) that makes for 3.5x6.3mm letters. Different encodings give you slightly different sized letters, but it's all roughly the same.

So I'd guess around 10 to 11 point.

Has this helped?