"I have the original ublox module 3DR sold (the one without the compass.)  It was advertised as able to update at 5Hz, but there now seems to be a new data sheet here:
  http://www.u-blox.com/images/downloads/Product_Docs/LEA-6_ProductSu...
that…"

"I'm wondering the same thing.  MY LEA-6H is configured to use a 200 ms update interval (5 Hz) but, when examining the iTOW field of the position record to see the timestamp between successive messages I see a difference of 400 ms, which is only 2.5…"