Similar strains would have to be grown along side similar wattage.
I have seen cfl's compared to HID's many times across these boards. I've even argued against the use of them without ever having any real experience of using them. I had a 250w grow king, anyway I sold it.
Obviously equal wattages are essential too. After that it's down to your nutes, environment and your personality (I believe that cannabis likes some people better than others, and will respond better because of this).
No limits on Co2 or enzymes things like that. Although a regular, well-documented log of everything MUST be kept, and updated here on rollitup. We now have seven challengers, that's enough for a forum, maybe one more...
I have my excuses for not taking part at the moment. My system is not running at full pelt yet and I'd like to get that ticking over smoothly first... maybe in a month. Although as I have said there are enough challengers to get a forum going, it's just that I don't think rollitup is completely sold on the idea just yet.