Updated: Sep 27, 2021
Intel's newest 11th generation CPU's have just hit the market, and with that the relatively new 'i9' nomenclature is even harder to differentiate between the traditional i3/i5/i7 lines. With this generation vs the previous 10th generation Comet Lake CPU's, the new flagship i9 has lost two of its cores- moving from 10 cores/20 threads to 8 cores/16 threads... exactly the same as the i7 variant. That 10-core configuration was previously the only real characteristic that earned it the 'i9' moniker over the 8-core i7 in 10th gen.
So this year, what the heck is the difference between the i7 (11700K) and i9 (11900K) flagships if they have the same major technical specs across the board, and why would an i9 deserve your money? Well, it comes down to just a few (three in total) subtly distinct differences- of very little consequence in the big picture. They are:
The Base Clock Frequencies
Intel "Thermal Velocity Boost" (i9 Exclusive)
Let's dive into the details below:
1. The Base Clock Frequencies
This is the most obvious difference, and one that's so minor I really don't understand how they can hang their hat on it to justify 'i9'. The main difference comes down to the turbo frequency, although the base frequencies are (pretty negligibly) different too.
i7 base frequency: 3.6GHz
i9 base frequency: 3.5GHz
i7 turboboost max frequency: 5.0GHz
i9 turboboost max frequency: 5.3GHz
But even though these are modest frequency variations to begin with, if you get the unlocked ('K') variants of the CPU's, you can boost these clocks easily and manually in the first place, making these stock clocks even more inconsequential.
2. Intel "Thermal Velocity Boost" (i9 Exclusive)
From Intel Ark Entry: Intel® Thermal Velocity Boost (Intel® TVB) is a feature that opportunistically and automatically increases clock frequency above single-core and multi-core Intel® Turbo Boost Technology frequencies based on how much the processor is operating below its maximum temperature and whether turbo power budget is available. The frequency gain and duration is dependent on the workload, capabilities of the processor and the processor cooling solution.
This feature was introduced in 10th Gen, so it's relatively new. Essentially, this is an extra boost setting that's configured to boost up to ALL cores to a set frequency- as opposed to Turboboost settings which only apply to 1 to 2 favored cores in a CPU. Intel TVP is set to also boost clocks slightly higher than where the Turboboost settings may be set.
It's kinda neat and novel, but again, if you've got a K variant CPU and you know your cooling can handle higher frequencies steadily, you can simply overclock your processor manually to the TVP frequency or above, negating the whole feature. But for many users that just want "something fast" from the factory and have no ability or desire to mess with the CPU settings, this is a pretty cool function that should safely and thoroughly give you more power without harming the life of the CPU as it'll only kick in when it's cool enough.
This is really the main selling point for anyone that is genuinely trying to figure out if they should spring for an i9 over an i7 this generation. Binning is the process of sorting chips off the factory line into kinds of ranks. A higher-binned CPU is going to be more capable of overclocking than a lower-binned chip. It's likely that the 11900K is specifically going to be a higher-binned variant of the 11700K's to earn it the 'i9' moniker. If you're in to enthusiast level overclocking or are curious about it, then the i9 may be the CPU for you.
You should achieve higher overclocks and more stability at those frequencies than the i7... but in the real world, you'll really want to run a modest overclock to preserve the life of the CPU either way... so real-life scenario, you might be able to run your 11700K on all cores at 5.5GHz 24/7... and your i9 at maybe 5.7GHz. This possibility is different with every single chip, it's a kind of lottery when it comes to overclocking and getting a known 'binned' part gives you better chances of successfully getting better overclocks.
But practically speaking, even if an i9 has a stability ceiling ~500mhz higher than an i7, in reality that's still not a huge bump (~10% with 500MHz), and as you approach a ceiling you really start stressing chipset and CPU componentry, needing voltage bumps, running into random stability issues and crashes over the years, and shortened lifespan of the motherboard and CPU in the long run.
Ultimately you'll want a modest overclock for a myriad of reasons (the ability to claim 'more speed' than stock, the free enhanced performance in almost all use cases over stock Intel clocks, better bang for your buck, and a reason to actually utilize your high end liquid cooler other than just having it 'look cool' if you have one). But either way, the binned-variant i9 would be able to achieve a higher overclock by at least 100-200MHz over the lifetime of the chip than the i7 in all likelihood.
This is all (educated) speculation as we're just on the cusp of the Rocket Lake 11th gen i7 and i9 release, but there is a lot of mysteriousness surrounding the relatively unusual i9 specs this generation so hopefully this makes it easier for you to decide if you are in the situation of building a new rig and tie breaking between the i7 and i9 models this year.