[thstone]

What you call the "hub spec", I would call the "center bore" or "hub bore".

All of my usual references show the same variation that you found (some say 71.5, others say 71.6).

Since every other Porsche (911, 912, 930, 964, 993, 944, 968, 924, & 914) is typically listed as 71.5, I'd go with 71.5.