Good news to report-my issue was card related.
I bought a Lexar 16GB Professional 400x CF card and nearly a thousand images later (a mix of RAW+JPEG and range of quality settings) I have seen no image corruption.
Thanks for the comments and suggestions.
The original SanDisk card came bundled with a 5D2 and 24-105 L from DigitalRev (in Hong Kong). Other than the card issue I was very, very happy with DigitalRev's customer service, speed and price.