iMac 2017 Ram upgrade limitations?

I have a 2017 27 inch iMac with a 3.4Ghz processor which I'm looking to upgrade the RAM on. Checking on the Specs on the support page here: https://support.apple.com/kb/SP760?locale=en_AU I noticed it only advises that it is configurable to 32GB. Despite there being four slots available and the other models (3.5 and 3.8Ghz) both able to configure up to 64.

I was hoping to fill the iMac with 4x 2400MHz Kingston DDR4 16GB RAM Chips.

Can anyone tell me why it's only configurable to 32GB and what would happen if I were to fill up the slots to 64?

Cheers,

K.