street boosting or highway boosting, no difference. Its mainly dependent on how long you were boosting and the time inbetween each hard run. It could be easily argued that street racing gets them even hotter because the lower speeds dont wisk the temp away as well as highway wind.
But, I have watched the temperature of my Z shoot up to 230 degrees and take 2-3 minutes to come back down to 180 degrees sitting there idling.