I am hoping that they aren't holding out for the 9th generation for the iMac although it does make sense. Losing hyperthreading in the i7 seems like a bad move by Intel. Unfortunately that ripples through to Apple. I wonder how a 6 core i7 9700K will compare against the i7 7700K currently in the iMac. Maybe Apple will use the i7 8700K. They may be able to order enough volume to make it worthwhile.
If they offered the iMac with the 8700K, I wouldn't be waiting for the Mac Mini.
More cores will always trumps hyperthreading...each core in the Core i7-9700K (8 cores BTW) will have 1.5MB of L3 Cache all to itself, no sharing. We have been conditioned over the years to accept that hyper-threading was
almost as good when it fact, it really is not that good at all. The higher clock speeds mitigated some of that over the years, but clock speeds are still stuck essentially at levels reached in 2005, which is to say, we haven't really broke 5.0GHz on any Intel CPU for day in/day out single-core clock speed yet. But, hey, the laws of physics, so natch.
The 6700K runs at 4.0GHz, 7700K runs at 4.2Ghz, the 8086K, runs at 4.0GHz and can hit 5.0GHz Single Core Turbo, but it is a limited edition CPU, so it counts, but it doesn't. Overclockers are hitting 6.0 GHz on all 32 cores with AMD's Threadripper, but that's with LN2 and no one is running that setup on their desk at the office or at home, so we're in a bit of a pickle. We have more (consistently higher sustained) clock, more cores, more cache, smaller transistors...yet, we really haven't made any gains that make us go WOW! I need that! GPUs are still doing that but, eventually, the uncanny valley is crossed at 240fps and then where do they go? 8K? 16K?
With all that being said, 8 cores is really the limit of usefulness to the consumer 27" iMac buyer, because unless they are transcoding, encoding, decoding, or have 4 arms and two brains et al. more cores and more thread have diminishing returns versus the clock speed penalties they can inflict to stay within a relatively energy efficient TDP. The Core X-Series runs the gamut from 4c/4t to 18c/36t and some very nice clock speeds, but with a 140wTDP.
The one CAVEAT here would be if you are a heavy VM user, Docker, et al. as being able to have 8 cores and parsing 2 or more to the VM without seeing much of a performance penalty or resource juggling (w/enough RAM) may help out those using Windows VMs or who have lots of Docker instances they need to debug and develop for while still keeping a reasonable amount for Xcode, Visual Studio, Eclipse, et al. Having an 8c/16t iMac on their desk without having to shell out for an iMac Pro leaves money for more DRAM, more monitors and more Mountain Dew (one dev I worked with was never without a Dew in hand).
If I were in the market for a new iMac, I would almost certainly go for the 8c/16t Core i9-9900K CPU, but that is just me...almost every Mac I own or have owned has the highest spec CPU Apple offered. That being said, I still love my 2.2GHz Base Model 2015 15" MacBook Pro. It may only have an iGPU, but it's an Iris Pro 5200, I get hella battery life and it never seems to run as hot as my work issued 15" w/AMD M370X. It seemed like Intel would be stuck on 4 cores or 4c/8t forever, not just the past 8 years and all it took was a little RYZEN to inspire them to pry open their wallets and spend a bit of R&D to give us non-enthusiasts 6, and now 8 cores. Thanks AMD...now please get to work on getting Vega Instinct into our hands and into Apple's.
