32gb kit and 64gb kit help on speed (HELP)

When selecting ram I was always told you can add memory later on however I just want to clarify something.

 

If I select a 32GB kit and 64GB kits in the memory selector the speeds are not the same. For example I can select a 36GB 3600mhz 4x8 kit but there is no 64GB kit for 3600. The speeds actually are lower with 64GB (little confused)

 

SO I can buy 2 4x8 36gb 3600mhz kits but something is telling me its not that simple since 64gb kits are slower in speeds. DO I sound confused lol

 

I was told at one time that you buy the kit you want, 36, 64 or 128 at one time for compatibility reasons but I also here you can add later....

 

If I buy 2 sticks of 16gb = 32gb 3200mhz, I can buy 2 more to make 4 sticks @ 64gb and the price is cheaper than buying 4 sticks for $50.00 more X 2 = $100.00 (EXAMPLE)

The more modules you add, generally the lower the speed you'll be able to reach. This is especially true if you're adding modules from a different kit, which is why we recommend getting the appropriate kit from the get go. You can still mix kits and have it work, but it'll likely all run at a lower speed (and require manual tuning) not counting any compatibility issues that may come up.