That blows about your cracked tank. You know how it happened? Hope there wasnt much damage/loss.
I believe the main reason why the WPG rule is obselete is because different lighting have different water penetration values, or intensities if you wish. MH are generally hailed as the best because they are the most intense therefore being able to penetrate through more water.
Remember that light travels in straight lines and gets weaker the further it goes. The more stuff it has to travel through, the weaker it gets. WPG would work if light was liquid and could dissolve evenly through water (dont we wish it could do that?)
Apparently the talk is that T5's are the new way to go due to its intensity, energy efficiency, size, heat radiation, price, etc. Personally, I'm considering going T5 from PC's. I'd like to see more testimonials (but to its credit, i have yet to see a negative review on T5's)