400W DE Metal Halides?

[Jaws]

I was just wondering if anyone can comment on the 400W double ended metal halide bulbs. I need to replace two out of four of my metal halide bulbs and I would like to upgrade my ballasts to a PFO ballast as well. I've got two Geismann 250W 20000K DE bulbs running off a dual 250W PFO HQI ballast now and the color is great. Since I'm planning on going for a bigger tank down the road anyways, I'd like to start upgrading to 400W halides now if I can. I noticed the PFO 250W HQI ballast is more expensive than the PFO 400W HQI ballast and I assume it must be better in some way. Can anyone point me in the right direction?