I only used the SRT Viper SRT-10 Coupe '06. Wikipedia has this car at 510 HP and a top speed of 192.6 mph which gives a calculated (effective) Cd = 0.329, seems about right.

Using the GT6 versions, horsepower, top mph, Cd:

900 HP, 215 mph, 0.417

800 HP, 207 mph, 0.416

700 HP, 199 mph, 0.409

600 HP, 189 mph, 0.410

500 HP, 178 mph, 0.409

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500 HP, 175 mph, 0.430

400 HP, 164 mph, 0.418

300 HP, 149 mph, 0.418

254 HP, 141 mph, 0.418

That's as low as I can go with 50% power limiter. Note even at 254 HP setting the Viper is still accelerating at one mile. Cd formula is consistent, shows PD used a fixed number, given the speed values are visually observed only.

Now compare 450 HP versions:

Sarthe 2009 no chicanes, 191 mph, 0.298

SSRX km 6 downhill, 208 mph, 0.231

SSRX backside, 195 mph, 0.280

So it looks like PD used a CD about 10% lower than actual, 0.298 instead of 0.329. SSRX seems wrong if Sarthe is right.

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