5 years ago I bought a MSI GT 70 20 D Dragon Edition 2 laptop with Partition C consisting of 3 Toshiba SSD 128gb mSATA in RAID mode. I would like to replace them with Samsung 860 EVO 500gb or 1tb mSATA Will it have a significant effect?
Significant Effect? - you mean aside from the space increase? That answer is NO. Even if you could upgrade to an NVME drive that is 5 times faster then your current setup, the increase is not often noticeable from the users perspective.
Aside from the 3 times more places the array could fail, loose any one of the drives and all your files are gone, I've been running 2 860 Evo's in raid 0 for over a year with no issues. I keep good backups and have zero concerns about loosing the array. If you get one or more of these, be sure NOT to get the "860 Evo QVO" . Those are Quad level cell drives and not suitable for use in raids.