Consider energy cost usage as a possible limiting factor. AT $.10 per kWH blended, I use 6 FPS as a good rule of thumb for standard black steel. For SS pipe, the cost is much higher for materials, so your economic model would tend towards a faster flow rate as being optimal, based on installation cost and future energy usage.
Above 8 FPS, other factors such as valve erosion may come into play. I am not a real expert as that stuff in a shoot from the hip way.
Steve