UHF

I only bought my car a few months ago (MY99 Turbo UK) and i knew they ran hot but I was out today driving up and down the A10 testing out my new sound system and although the dash board said that the car was normal temp there was some serious heat coming in through the windows. Now I know these cars run hot (I had a fiesta turbo before and even that was boiling up), but is it doing it any harm driving hard in this weather or are the cars designed for this, I left it to sit for 10mins and the heat was just pouring from the thing, its a standard car and i'm dead worried, help! Also I notice a terrible loss in power in this heat which I accept is normal (just how much power do us standard boys lose in this heat). Just after a bit of advice from people who have owned them for longer than me, just making sure i'm not about to kill my car.