General rule of thumb: iRacing attempts to mimic real life performance as much as possible - ergo, what you would do to a car in real life to affect performance will more or less affect the sim car's performance in the same way.

For example: tire performance is always going to be a balance. Yes, the game is coded to treat colder tires as having more grip, and more grip can equal faster lap times, BUT tires also have dimensional physics modeled... too little pressure and the tire edge can actually fold over, reducing your contact patch and thus reducing your grip. Also keep in mind that while less pressure generally equals more grip, this also means that your tires are heating up faster - and staying hotter longer - because so much of the tire is in contact with the road surface for more time. Increasing tire pressure will reduce rolling resistance and reduce temperature buildup over time, and it will be easier to cool off your tires if you need to, but you have less grip because of a smaller contact patch and your driving accuracy will need to be that much more precise to gain proper benefit.

To sum up, it's a balancing act; there is no "correct" answer because everyone's driving style is different. You seem to be one of those people who go into a game and just ask "what's the best car/item/gear/options that allow me to engage in maximum pwnage with minimal effort." Despite what you said in another comment, you DO seem to be asking for the exact iRacing attributes that result from their specific physics modeling equations so that you can just try to match up your car setups against those attributes and be fast without actually having to work at it and practice.

Now I apologize if that assumption is incorrect, but it really sounds like that's what you want.