This really isn't a comparison of Silverstars versus the VisionPlus bulbs, this is a matter of the fact that as most everyone knows, projector headlights do exactly like the name states, they PROJECT light. I'd estimate the light output of the Silverstars closer to a 20-25% light increase over stock bulbs. Even based on the lumens versus the stock bulbs, the yield is quite a bit more than 10%.
Human perception obviously is just like decibels with sound. Every 10 dB increase is an increase of 10x in sound pressure, however, humans perceive this as twice as loud. In order to make a sizeable difference in light output, obviously lumens is not a 100% accurate way to go but the light output is definitely improved over stock, more than 10%.
Just my .02.