It's hard to say with absolute certainty, but I think 2-3 years is a reasonable guess. 64GB DIMMs have only recently become semi-reasonable, and I still use a l

It's hard to say with absolute certainty, but I think 2-3 years is a reasonable guess. 64GB DIMMs have only recently become semi-reasonable, and I still use a lot of 16GB or 32GB DIMMs on smaller deployments. Basically whatever the top-of-the-line DIMM option may be (and this applies for CPUs and HDDs and other stuff too), you want to avoid being in a situation where you HAVE to use it. Vendors price these parts accordingly: you pay a premium for top-of-the-line because you must have it. If you can avoid that, do so.