Never hade such a problem with onboard RAID always do a RAID 0. Mostly I'm limited in speed due to the PCIe lane layout/configuration coming from the CPU or chipset and the DMI lanes on none HED systems (Intel). Definitely with fast external direct attached storage boxes in raid 0 and a 10 Gbit NIC .
Theirs no real life scenario that makes sense for me, doing more than 2 sata or NVME disks in RAID 0 on a system (with a x16 GPU) when looking at performance. The M.2 NVME disks are fast enough when combining them with sata ssd's in RAID 0 or external ones.
