What double precision exactly in graphic cards?

My configuration:

Gigabyte GA-770T-D3L (Newly bought Crosshair V but replaced yet)

Phenom II X4 955 BE (w/ Noctua NH-C14)

Sapphire Radeon HD 5830 Extreme (w/ Arctic Cooling Twin Turbo Pro)

GSkill Ripjaws 2x4 GB PC-10600 DDR3 1333 Mhz CL7

Corsair F60

Huntkey HK-700-52PP

I have some questions. I am thinking about replacing my gpu. But with which serie? 5830 has a double precision level about 300s. 6950 approximately doubles the 5830 at double precision level but it is so expensive. On the other hand 68xx cards are cheaper than 6950 but have no double precision. I have played Crysis 2, and had some slowdowns. Crytek advices at least 6850 for Crysis 2 which has no double precision feature. Now what i must do; upgrade (?) with 6850 by considering to have a card with no double precision or upgrade with 6950 (even 7850 w/ double precision) by emptying my pockets? Which one?

And another question;

Does double precision affect using some softwares which require multiple monitors, color variety, sharpness and transperancy? (Pro Tools, Cakewalk, Cubase etc.)

The last question;

Crosshair V has no Pci-e 3.0. If i buy a 7850, will i live any problem with 7850+Pc-e 2.0 interface?

there  is  way more important  (gpu) details then  just double precision  lol , if your gonna upgrade ,  make  it worth your while !  , get atleast a  6870  ,  but  if it was me  i would get a  hd 6970  ( prices have droped alot  on the (6000 series cards)  or better yet  get a 7870 

you never mention what  resolution  you play at  ,  if your  playing below  1920x1080  , most games will be more cpu bound  then gpu ,  either way  i hope your overclocking your  955  , (atleast you have a decent cpu heatsink )

and no   pci-e 2.0  will not cause any issues   or loss of performance if your  gonna  use a  pci-e 3.0  gpu  with your  mother board

and if your gonna upgrade your  gpu  ,  i would  get rid (upgrade)  that  pos  psu      cause  that  psu  has been known to  catch  of fire   , and destroy your hardware  wth it  when it  blows up !!    ,

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