thanks for all your help guys,

@alan
my max sample level is 1 and the min -1. I don't even now wether this is high or low. (sorry for my incompetence, but I am just figuring out that rendering is a science on it's own)


I've achieved a mildly satisfying render time. Mainly by taking most of my textures down to 1048 or 512. I don't plan any extreme closeups anyway. And not using final gather but global illumination instead. It renders nearly twice as fast with acceptable results.
The image below was rendered in 12mins, still a bit too long, but I will replace the textures of the background buildings with 128's. And play with alan's suggestion.

cheers