Yes, C_P, it's all speculative. But, hey, that's what's fun for me: speculation! I like speculation.
The wiki chart you linked to is a nice recreation of the warp factor/power usage chart found in the TNG tech manual, pg 55. The obvious errors of the original table (eg, "power usage in megajoules per cochrane") were corrected (eg, "power usage in *megawatts* per cochrane") in the wiki chart and the resolution slightly enhanced. It has its own problems, of course, but it's a nice one none the less. Indeed, it is from this very chart I used to calculate the power usages quotes for the Galaxy Class, above. And, yes, IMHO, I think it's safe to say the chart is for the Galaxy Class specifically. How that chart changes for different ships is up for debate... Which is exactly what I want to do!
...I just need to find a place that has done/is doing it. Which is why the question.
Thanks for the other links. I'll check them out when I'm not at work.