I do not know. I can see the reliability, but my KWA M9, and G23s, deliver strong rapid and accurate fire power down range every time I need it, with a much higher ROF than a spring gun.
My biggest problem with spring guns is that you must break line of sight with your target in order to cock the gun again. my GBB's don't have this problem.
I would say that a spring pistol could hold par with a poorly made gas gun. But a quality one such as a KWA or KJW? I dont think it would stand up. However, a spring gun would be cheaper than a gas gun on Average.
But I would recommend the KJW Mark. 1 ruger to anyone who needs a sidearm, its not what I use anymore, but it was my first gas gun. They are reliable, strong, cheap, and highly accurate for there size.