Re: All Graphics Cards related queries here.
to reduce the temps, try and clean up your system from inside including gfx card's HSF. the reason for drop in fps is not only your gfx card but your processor is also slow. also you are playing at such high resolution. so to improve the performance lower the resolutions and details or upgrade your entire system. also cm silent pro m850 is too too too much for this rig. your psu is not good for current gfx cards.
The sole reason is the Graphics card itself, Jaskanwar . Phenom 9950 is a very good processor and on per with Core 2 Quad 6600. P 9850 and 9950 are free of the TLB bug and also having 2 MB L3 Cache. You can check the review in Tom's Hardware.
If you wanna play WoW at full HD resolution with over 30 fps then minimum a Radeon HD 5650 is required. Get the 1 GB version. your current PSU will be well enough for it. If you want a little extra punch in all the games, then the choice is either HD 5750 or Nvidia GTS 450.
But if you can spend the money, then get GTX 460 768 MB @ 10.5k
Although your current PSU may support those cards, but a PSU upgrade will be advisable.
Also Phenom 9950 is a Black Edition processor and has good over clocking potential. Try to over-clock it to 2.8~2.9 GHz.
And regarding PSU, as Jas said, a 850 is a super overkill. Go for Corsair TX550
, more than enough for your configuration.