I also added M.2 recently. First of all not all M.2 will do great job. M.2 must be PCIE, NVME and should have good read and write speed. I used PassMark chart > Best value SSD 257-512GB to determine which one to buy PassMark Hard Drive Value Chart - Performance / Price of Hard Drives (harddrivebenchmark.net)
Result is that Puget Bench score increased for 50 points. Yes, M.2 will impact performance. I can not tell how much difference will create other SSD M.2 models (mine is WD Blue SN570) because I haven't tested them all but I am almost certain they are not all the same. Also there are M.2 SATA SSD which may not create big difference, just read what is read/write speed. When buying SSD check what is PCIE version supported on motherboard because ver.4 is newer and promises higher speeds, at least in the featuire. At the moment it is not offering much of the difference I think. Update: PCI Express version must match processor's PCIE version for full impact. PCIE is backward compatible but will run at lower speed. PCIE 4 will run on PCIE 3 slot if anyone thinks about later upgrade.
When it comes to memory I think that speed also makes some difference. From what I found on the internet, up to 3600 is sweet spot because beyond that latency will increase and benefit will be lost. Looking at Puget Bench scores it seems that same configuration gives better performance when running at 3600 memory speed then when running at 2666, for example. I am looking to buy Vengeance LPX 3600 2x16 CL18 DDR4 optimized for AMD. It is budget memory which is probably best value for money (11th in speed chart) according to UserBenchmark RAM UserBenchmarks - 113 Memory Kits Compared
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