I notice it on all my machines. The only way to not notice it is to be a damn liar, or not apply the patches. My XPS13 has an i7 8550U and it took a hit. Which pisses me off the most since it's #1 fairly new, #2 already a bit restrained because by design it is a low resource "U" class coffee lake, long battery machine and super power efficient. So I'm basically banking on some decent upgrades down the line to bring life back into a new machine that a few months ago was impressively powerful for this class.
My personal benchmarks that I use(because IDGAF about gaming, since maxing gaming for 99% of games is pretty easy mode, so for my tasks, takes a back seat to serious computing for production) consist of doing scientific hash assessments, just a great raw bench that nobody GAF about in the review-world unless they're hardcore nerd as well.
The XPS13 was at 89mh/s before (which is freaking great for a portable device) and 59mh/s after.
I have a bunch of older gens all over the map that are in my direct and extended maintenance. A ton of systems here, family systems, etc. I only have the one Ryzen system right now, and it is by far and away the lowest performance hit. Also helps that the bios allows PSP disabling without an extended workaround that doesn't fully disable to maintenance OS. Now it's not all roses for AMD, my old opteron system still took a good hit as well. The dual opteron server, while nowhere near as exploited, also took some hit. But in all fairness, that's a machine I should just upgrade already. It still holds up and ram is still too pricey. 76mh/s before, 68mh/s after.
The part about the Ryzen system that kind of sucks though, is if you wanted to not patch, take the risk and keep your old performance.. well, the bios updates expand on a lot of memory and m.2 compatibility. So you have to choose. I couldn't make a m.2 drive bootable no matter what unless I used a bios that included new microcode for specre workarounds(WD Black 3DNand, so something that came out long after the mobo, so I'm lucky it was patched to begin with). Before and after for scientific hashing, I did 146mh/s before, and 132mh/s after patching with 0 impact from any GPU or SSD change.
Wife's desktop is a 7600 non-K and she's not computer literate, but she noticed the difference and said it was night and day after it was fully patched. Never benched it, wish I had though. But if she notices these things, it's legit.
Sister has an older laptop(mostly a tablet user, so she's just trying to extend this one uptil we see another cycle of super cheap ram), IIRC, a socket P 8600(which is a core 2 duo platform, not coffee lake). Had to switch her from antix to Vector Light(ultralight linux distros that thrive on older machines) Antix is a 128mb *rated* kernel in memory OS, and VLL is a 64mb *rated* kernel in memory OS. Puppy, which is light, not ultralight, is IIRC, a 512mb *rated* kernel in memory, so you can imagine just how far down the rabbit hole this has gone just to save a perfectly functional machine for the purposes of ... checking facebook, email, and watching youtube/prime/netflix videos. While it would run all those things fine unpatched, patches made it impossible to have more than one window open at a time in a 'mainstream' web browser. I switched her to Brave for media heavy sites and midori for email and text heavy sites, but even Brave isn't a silver bullet.
The amazing thing... it's not just x86. Any reasonable ARM device that has actual security patches possible also took a noticeable hit in performance. Yeah yeah, stob being n00bish and focusing on phones/tablets here, think about ALL the ARM devices you have. From your TV providers set-top DVR and complimentary cable boxes to your routers, modems, automobile CPUs, IoT devices, etc. People that have installed security cameras that stream to a cloud provider that once could handle 5 cameras safely can now only capture data off 3 at the same bitrate and frames. That is a HUGE drop and it's no wonder people leave their hardware unpatched.
So yeah. If you're not seeing much of a hit with recent CPUs, then it's because your system isn't fully patched by your own choice, or the manufacturers have not fully released patches or bios updates.