2017 27" iMac accepts 2666mhz Ram.
Testing with a 2017 iMac, thought i'd see if it'd take 2666mhz sticks and assumed it would and clock them down to the 2400 standard Apple advertises and sells, instead, it actually runs them at 2666 (reported as 2667mhz in macOS as it likes to round things up)
Thought it might be interesting for some - I didn't run a benchmark on it yet but I will in the future - in the UK currently 2666mhz ram is actually cheaper (the 2400mhz have gone up 30% from retailers since the iMac launched)
I suspect it'll run lower clocked ram easily too (the 2015 model did) and it'll probably run 3000mhz ram, if not at 3000, at 2666mhz no problems. So more options to shop around.
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