James
Things have changed since 2009 and that information is no longer relevant, with the Mercedes power advantage on the straights, Istanbul could be reaching much higher speeds if F1 went back there, same with Valencia.
back then the ERS systems were not as advanced nor was there a good DRS system either, it was a blown device and they had diffuser technology battles going on.
i would imagine with the differences in Aero and tech and Mechanical side of things i bet those speeds could reach upwards of 330kph for Instanbul and 345-350kph for Valencia. But that is what we can assume as things have changed enough where no one is certain. But you can be sure that William F1 team have known to be the fastest thing in a straight line at some events and the speeds they record are unbelievable.
I don't know about you but i've never seen an F1 car go around Monaco in the current configuration and do 235mph, that would be beyond any sense of these physical laws and so on.
Next years cars are going to be more mechanically advanced due to the larger tyres as well, so the chances of faster cars are going to be a lot higher, so 380 kph / 235mph is around good enough and it should only be done at specific tracks.