SSD is more than an order of magnitude (or much) faster than SAS high-rpm disks.
SSD is limited - usually to 1-2 TB of storage. With 128GB of memory, you could easily use SSD disks to load whatever file you want into memory - e.g., usual term is a RAMDISK. Ubuntu supports this. It also caches files very effectively without much human intervention other than configuration.
Learn about pdflush:
The Linux Page Cache and pdflush
There is also vmtouch. You can force any file to be read entirely into memory. Which would definitely favor SSD.
https://hoytech.com/vmtouch/ Also note some other tools on that site.
So, I would suggest: SSD's and vmtouch (or an analagous tool.)