I can cofirm that problem with light sources, they are effectivelly lowering my fps on minimal settings too, but I don't have problem with long loading time (yet?). I have laptop with i5 3210m running 3.1 Ghz while playing, gt635m 2 gb DDR3 (should be enough), 8 gb ram (more than enough I think) and windows 7 pro. I am using latest drivers ofc and my disk is defragmented regulary.