Actually theres not much of difference between using psos or vxworks.A few differences in features are:
latency<4.33 microsecs while psos its higher.
Other then these both work in same manner and follow same
Also as psos is getting killed no fresh development work is supported by windriver for psos. Also vxworks development environment is much more user friendly then psosenvironment becos vxworks IDE mimics mostly visual studio.