I don't calculate the temps.
I notice the performance loss as I ride.
The biggest loss isn't from pre-ignition,
Getting higher octane fuel is not going to help the performance loss at hotter outside temperatures, because it's not nearly as hot that the engine is pinging, or else the engine temperature should rise, and it doesn't.
Getting hi-octane is only going to help if you get BP or Shell premium, as they have nitrogen infused fuels (burn harder).
Shell gives about 5% and BP 10% more power, or efficiency, depending how you ride it, but that's also true for other vehicles without turbo or intercooler.
Even scooters benefit from the same power increase.
The power loss is not linked to the use of 87-octane fuel, but from hot air, being less dense, entering the engine, thus the FI system injects less fuel to keep the correct A/F ratios, that results in the biggest loss of power.
Despite the air being hotter, which would promote pinging, it is also less dense.
And with less dense air and fuel in, compression will result in less PSI than when air is colder and denser.
Part of cooling that air more down, will help make it more dense.
And the hose between turbo and intercooler is the area where most heat can be soaked out of.
As far as high RPM,
I notice that at 80F, the turbo kicks in at just over 2000RPM, to ~2700RPM.
At 100F, it kicks in around 2500RPM to 3000RPM.
As the air is cooled in the intercooler, it shrinks, and probably causes a pressure drop; forcing the turbo to reach higher RPM to be effective.
As for engine RPM, on the on-ramp to the interstate, to 75MPH, in 5th gear, that will be 3500RPM.
I know that the engine doesn't perform well above 3k RPM, so I always try to keep it under. But it has almost no acceleration in 6th.
So the added engine friction and heat losses in (manually forced) 5th gear, compensate for the added torque compared to accelerating it in what the automatic gearbox would recommend in 6th gear.
Even at 105F, 6th gear functions well to maintain speed, but it no longer has any overtaking power, or acceleration at these speeds.