Low In-game performance on gtx 580 GXT 1536 mb .

im playing Cities XL right now , and something very annoying is going on .
( by the way happened in a couple of other games too )
but .. whenever im starting a new game , everything goes smooth as it should , but after a couple of neighbourhoods im building (lots of objects to render) , it becomes impossible to play ! fps drops to something like 20\19 .
and i seen the benchmarks for this game a year ago , the best performance was on gtx 480 ! with 40 fps Min !

and the weirdest thing is , that when im exiting the game , my gpu fan works as in idle mode( i can hear the difference , in BF3 it's god damn loud as Jet ) , and the gpu mhz usage is really low , almost as when im just browsing my PC .

any ideas?

Having you contacted nVidia? Sometimes certain programs and games will have issues with their current driver set. I know with ATI every monthly update usually includes various performance gains and fixes for a variety of software, more specifically, games.

Its possible updating your driver to the latest (if you havent) or contacting nVidia might be your best bet. You could help them uncover a driver issue...(this also can apply to certain settings, and not others. For example you could get awesome FPS at 1600x900 but horrible at 1920x1080...)

thanks man i'll try to contact them !
because i really dont think updating drivers will help because it's 2011 game .