That chart is WAY off and not close to an optimized set up. Any chart that predicts an ET from HP is not going to be good because how a car 60's is going to be a bigger determinant in ET. If it said you'd run X mph, then yeah I'd be more open to the chart, because it's harder to fudge that number.
Explain how this car, ran 6.94/96 in the 1/8 mile which is about an 11.00-11.10 with no more than 480FWHP. Extrapolating it would require about 550hp, yet it runs better, WHY? The car 60's, 1.43, like a 10.00-10.20 car. I'll guess if it was put on the transbrake, it would have gone 1.40 or better.
Video 1
http://imageshack.us/photo/my-images/13/irwindalevids002.mp4/
Video 2 6.94 run
http://imageshack.us/photo/my-images/13/irwindalevids003.mp4/
It's more about how the chassis works and converter efficiency than it is about raw HP. Watch pass time to get an idea about big HP claims and junky running cars.
A 420hp 340 set up right should run 11's in a 3200-3400# car.