Things are looking good for the 2018 iMacs. You can get a base model Coffee Lake Intel 8th Generation 6-core i5-8400 that will beat the current top of the line i7-7700K in most tests. And even when it loses to the 7700K, it's usually quite close in performance. Furthermore, the i5-8400 is a 65 Watt chip so it should remain quiet under most usage, unlike the very hot i7-7700K. But if heat and noise don't bother you, you can also go for the i7-8700K, which wipes the floor with the i7-7700K. All of these also include Intel Quick Sync, with full hardware 10-bit 4K HEVC decode, but the 7xxx Kaby Lake series already includes this. (The 6xxx series does not. 8-bit only.)
https://www.anandtech.com/show/11859/the-anandtech-coffee-lake-review-8700k-and-8400-initial-numbers
Too bad I couldn't realistically wait another year. I would have loved to get one of these i5 chips in an iMac.
I was expecting some other chips like an i5-8600 non-K and/or i5-8500 non-K, but haven't seen any mention of those. There is an i7-8700 non-K, but I suspect Apple would reserve that for the 21.5" iMac or equivalent.
https://www.anandtech.com/show/11859/the-anandtech-coffee-lake-review-8700k-and-8400-initial-numbers
Too bad I couldn't realistically wait another year. I would have loved to get one of these i5 chips in an iMac.
I was expecting some other chips like an i5-8600 non-K and/or i5-8500 non-K, but haven't seen any mention of those. There is an i7-8700 non-K, but I suspect Apple would reserve that for the 21.5" iMac or equivalent.