Readyboost filters small (~4K), random, oft used files onto media with lower latency than the main drive.
The 2 drives then read/write files they are best and fastest at handling, at the same time.
ie: A sort of ‘optimised for drive characteristics’, RAID 0…

Now look at the random 4K read performance of Optane versus SATA SSDs and even NVME SSDs:
https://www.google.co.za/search?q=optane+4k+random+write&safe=off&source=lnms&tbm=isch&sa=X&ved=0ahUKEwib_bSaqNHTAhWqB8AKHdxABmcQ_AUIDCgD&biw=1536&bih=798#safe=off&tbm=isch&q=optane+4k+random+versus+sata+ssd&imgrc=_
Writes are not as impressive as random writes go into the DRAM cache on the SSDs, but:
> This info can be lost in a power outage, so safer.
> The low write speeds are only valid until the DRAM cache is full.
> There should be an increase in SSD life as info is written to flash in 2-4 MB blocks
nowadays.

I think it’s worth testing to see if Readyboost does a better job than Intel’s RST due to this filtering/Optimised RAID 0..?

Info on overriding MS’s Readyboost settings, to test this:
https://hatsoffsecurity.com/2015/05/31/force-enabling-readyboost-windows-78/
But will anyone? The ‘not invented here’ force is strong in humans! 🙂

Romex:
Everyone knows that with your software installed you basically end up using a HDD benchmark to benchmark RAM.
Untick ‘Direct IO’ in Atto and MS’s Super/prefetch makes your block cache look stupid.
Can your software do predictive caching, without wasting RAM by caching what’s already cached by prefetch?
ie: Write software that switches on Superfetch with SSDs and add your SSD-saving ‘deferred writes’ and I’ll buy it!
I will say that your caching of HDDs to SSDs is very good and universal, so if one wants to cache any HDD onto any SSD, or even RAIDed SSDs; PrimoCache is the best option.

https://www.romexsoftware.com/en-us/primo-cache/

Romex Primo Caching Software accelerates all read / write operations with RAM and SSD caching, turbo charging any CPU to run just as fast as the RAM can go…

People keep trying to fix the Hard Drive speed bottle neck in hardware,
when it is much easier to fix in software, and RAM caching…

Primo Cache works similar to the Intel device. Say you have 32GB of RAM,
set aside 16 GB for a super sized RAM cache – all read / writes work at RAM speeds.
Primo Cache pairs ANY SSD device to the RAM cache, for a second level of persistent caching. All the stuff you use all the time, is copied to the SSD.

On boot up, the SSD reloads all your commonly used info into the RAM cache,
and the RAM cache dynamically updates itself to constantly keep you at top speed.

Go ahead and hook up your favorite 8 TB Seagate Drives to your system…
PrimoCache ensures your Big Iron hard drives run at RAMming speed.