it should be caveated here that nothing will stop you from inserting more than 64GB or ram. The problem is whether or not the system will physically recognize it. Plus, unless you are storing your OS in the ram using it as a ram drive, there really isn't any big benefit to having more than 32GB of ram IMO. There may be a few applications out there that might take advantage of it but for the average user using average programs, anymore than 32GB of ram ends up for bragging rights more than anything else. I currently run a 4 x 4GB ram setup on my I7-5820k. All my ram is PC-3200 Dominator platinum and I have not seen one instance with software utilities where my ram became over burdened or full. However, I mainly use my PC for games and writing code and at most I see only 75% memory utilization.
Wrapping all this into a neat little package. I will never tell anyone not to try something. I will only ever stress my own experience. Yours may be different however which makes for interesting debate. I am however interested is seeing if there is actually some benefit to high amounts of ram.
Another user stated that high amounts of ram over stresses you systems memory controller which is absolutely true. Another point to mention here is that ram in DDR functions in a similar manner to the way a RAID- Stripe does in hard disks. The CPU essentially writes data to all the ram sticks in bit blocks, while going through the sticks consecutively one after the other. RAM writes themselves essentially are a one step operation where the ram is written completely full before writing out to the hard drives pagefile.sys and the overall time it takes the ram to complete one operation (fill till full and empty to pagefile.sys) constitutes what you could call the RAM's refresh rate. Smaller RAM amounts, typically refresh faster but require increased operations when working with high work loads that adds increased overall work time. The opposite is true with large quantities of ram where RAMS ability to refresh is slower but it can handle high works loads much easier. Overall, its about finding a happy medium for your own use. Typically speaking, 4x4gb or 4x8gb tends to be the sweet spot for most people. These folks running 64gb or 128gb of RAM may have a specific use for that so I will not denigrate them. It's all about what best suits your use.