Nice work lucid, you have quantified nicely exactly the basic physics that we all (many of us at least...) understand quite well.
Those asking about the CSL the answer is indeed obvious - tires make a huge difference and that car comes basically with street legal race tires. That being said the CSL may be below the curve fit without those tires. Cars below the line are in a way the best designed and engineered cars for going fast, those above less so.
This also makes my point perfectly about the Nissan GT-R. I have sloppily added the car to you graph (man that was harder than Excel - I should have just asked you to do it...). The GT-R is an massive outlier in the data. This means one (or more) of a couple things to me.
1. They have really reinvented the sports car and bested everyone by a significant margin. Maybe it could be their AWD system.
2. The car is under rated in term of power
3. The car is under rated in terms of weight (claimed>actual)
4. The car had street legal race tires
What is the most likely scenario. I'd vote in order 4,3,2,1.
Lastly, bringing it back OT... I have added the new M3 at 7:57 and 8:03 (with US hp figure - 414). Again 8:03 is a provisional time and 7:57 is a good rumor directly from Richter and both times are still up in the air as to which tires are invlolved.
Nissan, BMW, whom ever, you simply can't beat physics.