Creating ambient light in to a city

I need to create similar lighting to a scene. I’ve tried GI and Area light, but the render times are quite big at that point, 4 minutes a frame. Need to cut down to about 2.30. And i need to render some animation at these settings. I Know that GI would be very good for this, but I havent found any good settings for this. Could anyone help?

http://www.darnellworks.com/a52/media/ishare2l.jpg

*edit: edited the post for a better referece picture.

well, without looking at your settings you used, its hard to help much. Theres alot of leeway in settings and how they will affect final render times. I dont think your going to find a faster approach then GI, unless you wanted to use some fakery, which for a complicated city, your looking at alot of work to look right.