RAM speed vs Capacity

We are looking to upgrade our RAM however have found that our server Motherboards limit us in a way,

The limitations mean we can either fill up with 32GB of ram however it will only run at 800mhz,
or we can use 16GB and reach 1333mhz,

My question is, speed or capacity?

Our servers are rather heavy usage as its the backbone to the business, will we ever use 32GB?