Just for the record:
Have a TT GO 630, use GO 9.510 navcore 32 MB.
Have a big SDHC Card 32 GB extern, and have all my maps in that single SDHC card.
But be sure to buy the right SDHC Card.
ECT:: Sandisk SDHC Class 4 32GB, or Sandisk SDHC Class 4 16GB, or Sandisk SDHC Class 4 8GB