If I have 2 SSDs via SATA3, both reaching speeds of about 500MB/s, which is close to SATA3 limit, does it make sense to combine them using RAID0? I mean if the SATA3 chip can provide the 6Gb/s speed for all devices separately, there should be an improvement, right? Any experiences?
does it make sense to combine them using RAID0?
No. The complexity of setting this up outweighs its usefulness.
If you want to achieve a major speed increase, upgrade to a motherboard with a new M.2 slot and put in an appropriate M.2 SSD.
A current - and not that expensive - Samsung M.2 SSD achieves a maximum reading speed of 3.4GB/s - far more that a RAID-0 of two SSDs with 500MB/s can achieve.
Concerning the problem of the TRIM-command and a SSD RAID-0 this SuperUser question may add further information.