Max memory for Optiplex 780

Hi,

We have Optiplex 780 mini-tower machines at work, and for the last couple of days want to upgrade them to the maximum memory possible. It's next to impossible to find an easy answer to what is the maximum memory is for these machines.

Dell specifications - http://support.dell.com/support/edocs/systems/op780/en/SM/SM_MT/specifications.htm - say it's 8GB DDR3 1066GHz

Two other documents on Dell website have 16GB as max memory.

Dell Optiplex 780 tech guide pdf (http://i.dell.com/sites/content/business/solutions/engineering-docs/en/Documents/optiplex-780-tech-guide.pdf) - page 9, and  Dell Optiplex 780 Setup and Features Guide pdf (http://support.dell.com/support/edocs/systems/op780/en/SFITS/SFITS_Al/SFITS_EN.pdf) - page 7

Anyone knows what's the correct information?

Size - 8GB or 16GB?

Which speed - 1066GHz or 1333GHz?

thanks

oliver