Memory Configuration in Precision T5500

I have the following configuration in my Precision T5500 BIOS

Memory Installed = 30 GB

Memory Speed = 1333 MHZ

Number of active channels = 6

DIMM 1 = 4 GB - 1600 MHZ

DIMM 2 = 4 GB - 1600 MHZ

DIMM 3 = 4 GB - 1600 MHZ

DIMM 4 = 2 GB - 1333 MHZ

DIMM 5 = 2 GB - 1333 MHZ

DIMM 6 = 2 GB - 1333 MHZ

RISER DIMM 1 = 4GB - 1600 MHZ

RISER DIMM 2 = 4GB - 1600 MHZ

RISER DIMM 3 = 4GB - 1600 MHZ

Having said that can I improve the configuration? if I was to change DIMM 1,2 & 3 with 4GB - 1600 MHZ modules will it make any difference other than the total amount of memory increasing to 36 GB