I haven't overdriven yet. However, reading over and over this article, leaves me wondering what could be achieved ODing using several single bulb ballasts. I have 4 of them. Do you think that could overdrive actual 2x? I mean, actual 64 watts into one bulb with two ballasts?
I fear, without a solid basis, that two ballasts won't work in perfect sync, and cause some serious strike or shock.