First I am sorry that I don't have regular SATA SSD to compare.

Side by side comparison. Left is HDD alone , Right is HDD accelerated by Intel Optane Memory.

https://www.youtube.com/watch?v=50QmSyQHBjc&t=510s

Test perform with i7-8700K @ 5Ghz , Sims 3 with all ep / sp and 6000+ CC.
It is 11.33 min loading times for normal HDD vs 4.15 min for HDD accelerated by Intel Optane Memory.
So what is Intel Optane Memory ?

The concept of Optane is like SSD caching back in Intel Z68 chipset / year 2011 era. Back in the day SSD was very expensive (128GB cost $250+). Intel release software called IRST (Intel Rapid Storage Technology) so user can buy cheap but small capacity SSD (32-64GB) to accelerate their HDD by way of caching. But as the time progress not many people use SSD caching anymore because SSD is cheaper and offer with more capacity.
Fast forward to 2017 Intel release Optane Memory. Although the concept is the same as SSD caching in 2011 but the Optane itself is different from normal SSD as it come with new technology called 3D XPoint (pronounce 3D crosspoint). It perform a lot better especially in random performance where it matter the most for consumer and it also offer much higher endurance than normal SSD. Optane is very expensive piece of hardware so Intel offer it in 2 forms. First is the real SSD called Optane 900P and 905P. Can you imagine about it's price ? Well the 960GB Intel Optane 905P cost 10 times !! higher than the cheapest 1TB NVME SSD name Crucial P1 ($1000 vs $100). So the price is far cry from most people's wallet. Intel solve the problem by releasing Intel Optane Memory for the mass instead. It come with 16GB and 32GB capacity at tiny price (as of 2019). It work by caching frequently used data to itself so normal HDD can feels fast like SSD.

Bonus. I later bought NVME SSD to test again. But this time I didn't record side by side and make a chart instead.

https://www.youtube.com/watch?v=8k6kpvIEM8Q&t=40s

It is Transcend PCIE 220S 1TB (3500 MB/s read , 2800 MB/s write).
Surprise ? A thousands read and write megabyte per sec didn't help at all ?
Why ? Like I said before thing that matter the most for normal consumer is random performance NOT sequential performance. Those thousands MB/s is sequential.
So what is sequential workload and what is random workload ? For easy understanding sequential is a big file but small in numbers while random is small files but there are tons of it.
These highend NVME SSD have only 70 MB/s random read performance at queue depth 1. (Most consumer workload don't go beyond queue depth 8).

So in the end you don't really need highend NVME SSD for Sims 3. SATA SSD 500 MB/s will also get the job done.

Record since 2013 with Plextor M5P SATA SSD 128GB. But at that time I only have a few hundreds of CC and also use small house with single household to test.

https://www.youtube.com/watch?v=2opucq6nF5w

Currently you can find 1TB SATA SSD under $100. Unlike in 2013 where you can only got 128GB for the same price !!

I think you can safely say my PC is no longer new.....it's 3 years old next month. I've got two 512gb SSDs (465gb usable) that I believe I paid about €260 for. They're a bit small for me, in fact there's barely 150 gigs free between them. I'm not really sure about what this all means but I've heard of RAMdrives, and I'd be able to run a full install of TS3 on 64 gigs of RAM. So I think it's pretty clear that for my next PC I'll want double the drive space, and 4 times the RAM.

SATA III SSD will do job just fine anyway - at random 45-60MB/s read (common result for current consumer devices) you'll hit processing power limitation of the consumer level CPUs and game programming faster than IO bottleneck (the game while reading a save does a lot of things).

Optane is kinda weird Intel innovation, perfect for the different times, for real benefits you need HDD (on SSD benefits are questionable, yes it will speed up random IO within the buffer frame, but any god help those who will start to make big transfers, with spinning drive however, the benefits are high) and because of PCI drives prices going down - slowly but still - it missed it's time.

You are correct. Once removing storage bottleneck CPU matter a lot.
I tested with i5-2500K several years ago and simulate different Ghz. I remember at 5Ghz loading times is shortest and 2.5Ghz is slowest.
Maybe I should try this test again with modern CPU.
I remember Sims 3 loading times only scale with Ghz not cores. But not long ago I try Civilization VI and saw a really BIG boost in loading times with more core (from i3 -> i5 -> i7 -> i9).

It's 2 thread game, really, what would you expect? And I suppose the IO is done in one thread for simplicity, just like the data is stored as plain pointer reference instead any viable database matrix, so the processing power limit is very easy to hit and multicore CPUs, which BTW just lately (the low voltage line) has risen above old Ivy Bridge with raw power, won't help much in that.

Intel Optane Memory does make your windows and game loading faster but it will mess up your hard drive.
I was reloading windows 10 once a month, then I disabled Intel Optane and no more hard disk corruptions. It usually happens if your game locks up. Oddly, the lock up doesn't happen as often if you disable Optane.
tl:dr One user believes that IOM is the work of the devil, or at least, not well implemented.

Shouldn't, either drivers are messed up or Windows screwed, again (what a surprise ... ). Data loss (it's cache, whatever left not properly unlinked will be lost), not closed safely files (free flying pipes 'till scheduler put them to order) yes it may happen. It's not easy to really mess up an actual version of NTFS, it's slow, obsolete and cumbersome, but quite resilient.

I can't use it because my processor is an i5-4460. Darn.