My questions are: Will this make the system unstable or be negative somehow? Is it a wise idea to set up the global performance cache in raid0 with a pair of SSD's? Or, is there another setup that would be better?
I have done a fair amount of research about SSDs in RAID0 configuration and have come to conclusion that speed gain is not linear. Unlike mechanical HDDs, you do not automatically double read/write speed when SSD drives in RAID0 are involved. You will have better luck buying SSD PCI solutions like OWC Excelsoir or OCZ Revodrive. By using RAID0 you also lose TRIM support that is supposed to keep your SSD drives healthy.
Right now I am in the process of building a new PC for AE and Cinema 4D as my 2-year old iMac is struggling and has no PCI expansion options. I decided to use the following storage configuration:
240GB SSD for OS
4 x 750GB 2.5" HDDs in RAID10 for storing projects
240GB SSD for rendering output
120GB SSD as scratch disk