Size does matter, unless the size is all taken up in length. Width and height (two important aspects of size) affect frontal area, and it is frontal area multiplied by the drag coefficient that actually gives the drag area, which is what causes the aerodynamic drag force.

Technically, weight also matters, but very trivially (to the point of being neglected). More weight causes more normal force on the tires, so more rolling resistance. Plus more weight load on the frictional surfaces of wheel bearings and such. That's neither here nor there. But the size does matter.

Size is why a Tahoe with the same drag coefficient as the new Camaro won't come anywhere near it in highway fuel economy.

EDIT: Also, almost any car will create lift at speed without the aid of wings and/or underbody aero devices. A car by necessity is more or less flat on the bottom (like a wing) and more "rounded" on the top (also like a wing) to create a greenhouse for people. Wings are often added just to get rid of lift and return the characteristic to basically neutral. Not too many cars actually use enough aero aids to add downforce (not just the absence of lift, but actually pushing the car down, like a race car).

 

Yeah, we're talking about theoretical stuff here - what I'm getting at is the 3rd and 4th gens have demonstrated that they have a low enough level of lift to where, independent of bumps and traffic, they don't fly up into the air or lose all ability to steer at such speeds. I'd like to know what the 5th gen does.

Jaguar took the new XFR to Bonneville and in near stock trim ran 225 or 226 mph. I presume the 5th gen can't do that, but it would be interesting to know what it can do in such a professional driver/closed coruse environement.

 

Based on a frontal area of 22.3 square feet and a coefficient of drag of 0.34 (that's what I found for an '08 Z06), 198mph requires 392hp at the ground.

Based on the same frontal area and a coefficient of drag of 0.36 (that's what I found for the ZR1 -- it's higher due to different front splitter and other aero tweaks), 205mph requires 461hp.

These numbers are considerably less than what the LS7 and LS9 can put down at the appropriate RPMs, which I believe is due to the gearing difference in 6th (relative to a dyno pull done in 4th) is responsible for the reduced power.

Interestingly, the drag coefficient on the base C6 is only 0.286. If it had the traction to get there, that would require only 366hp to the ground!

All of the above is assuming that we're at sea level and the temperature is 20°C (68F). Air density plays a significant part in the equation.

 

Wow, I had no idea the base C6 was so slippery! That explains the amazingly high top speed numbers.

 

I believe those tops speeds are reached in fifth gear. 6th is to tall (for the base and Z06 for sure); I am not sure about the ZR1.