You can get a 2400MHz DDR4 64GB kit for $470.
https://pcpartpicker.com/product/THzZxr/gskill-memory-f42400c14d32gvk
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I'm a pro user, have had my own Mac tower since the 120MHz 8500/120. My next machine was the 800MHz G4 Quick Silver, I moved to a 24" White iMac because it was cheap, and it was a great graphic design machine. When I got into photography, it struggled, and I upgraded to 2009 2.66GHz Quad core. It has 8TB of storage, an SSD boot, Sapphire HD 7950 Mac Edition and 24GB of ram (it's triple channel for some stupid reason).
I've been waiting for a good Mac upgrade that'll give me a worthwhile performance boost for my money if I spend $3,500. With the iMac part of the cost is the display, which I don't need/want. And once you get into the iMac, anytime you want to upgrade your machine, you always have to pay for a new display.
I don't want another quad core, as it's limiting with Capture One Pro 10, especially if you're multitasking - exporting files C1P, and finishing files in Photoshop. With a quad core, the speed comes to a grinding halt. Even a 6 core would help, as C1P could utilize 4 cores, and PS would only need 1 or 2 cores.
the 64GB Ram upgrade would add another $1,200-$1,500 to the system if upgraded through Apple. I can get 64GB of the same speed 2400MHz DDR4 RAM for $470. It's not ECC, but not everyone needs ECC nor a Xeon processor for their work, yet they still want more than 4 cores (so the regular iMac really isn't an option). And it's a HUGE leap from the $3,400 price of the 2017 regular iMac up spec'd last night, to the $5,000 8-core 32GB iMac Pro.
There is a GINORMOUS hole in that line-up. As much as I love OS X, It's not worth that kind of price for me. Not anymore. Apple priced themselves out of a LOT of pro user's wallets.
This freaking sucks rocks.