i tried using 2 tar ballasts to drive 1 bulb and I popped the breaker
the only thing I found with overdriving is you completely kill the lifespan of the bulb. however, for a $5 bulb to last 3 months versus a $40 to last 12..it's still kinda worth it. I found the CRI to be crummy in the $5 bulb compared to the $40 VHO bulb though..the colors in my corals and fish were bland, whereas the VHO bulbs made the colors amazing. that is when I gave up trying to cheap out on bulbs.