Raid-0 has been over hyped as a performance enhancer.
Sequential benchmarks do look wonderful, but the real world does not seem to deliver the indicated performance benefits for most
desktop users. The reason is, that sequential benchmarks are coded for maximum overlapped I/O rates.
It depends on reading a stripe of data simultaneously from each raid-0 member, and that is rarely what we do.
The OS does mostly small random reads and writes, so raid-0 is of little use there.
There are some apps that will benefit. They are characterized by reading large files in a sequential manner.
Raid-0 is actually very simple. Stripes(of user defined size) will be alternately written to the devices. If the devices are of different speeds, that is ok, like one half on a SSD, and the other half on a HDD. When it comes time to read,
the ssd stripes will be read faster than the HDD stripes. Where raid-0 potentially can be faster is when the app reads data sequentially, and has the ability to read ahead, thus overlappintg the i/o to the drives. Few apps actually are coded this way, so the benefit does not show up in actual usage.
A real drawback to putting a SSD in a raid array is the loss of the trim command.
I suggest the best strategy is to use the SSD as an os and app drive, and use the HDD as a storage drive for large files.