This is the underside shot of the exhaust of my IS-F
If you say that the vents on the IS-F are fake you're wrong. It's used to vent the heat that the engine generates. If I run my car very hard, this car gets very hot. Any additional cooling ports would allow heat to escape. Now the M3 has vents as well. Are those for cooling the engine too? or are they ornamental?
I'm pretty sure on a highway run... side by side, the F will pull on the M3 slightly.