i was wondering which gpu to buy XFX Double D FX-787A-CDBC Radeon HD 7870 GHz Editi... or SAPPHIRE FleX 100354FLEX Radeon HD 7870 GHz Editio...
i will be using more likely for workspace of 3 lcds then some gaming as diablo3, BF3, civilization and for photoshop and corel draw,,
i have 2 LCD 22" 1680x1080 and 1 LCD 24" 1920x1080
You don't have to have Sapphire Flex to use three monitors. All versions of the 7870 and 7950 will support at least 3 monitors, though one of those monitors will have to be connected with DisplayPort, you can't do 2 DVI and 1 HDMI. The Sapphire Flex edition is more for people who want to hook up more than 4 displays to a single card.
Spending more on the 7950 will net you more performance in Battlefield 3, but won't make a huge difference in Diablo 3 or Civilization V at your resolution. (I assume you won't be gaming across all three displays, as they are different sizes and resolutions)
Unfortunately, one of your monitors has to be connected with DisplayPort, it's a design limitation with how AMD does multiple monitors. Only two displays can be on DVI and HDMI, the rest have to be run through DisplayPort. The 7870 Flex Edition found here does come with a DVI to Display Port adapter, so you wouldn't have to buy an extra cable, just plug one of your DVI displays into the adapter. There is also the 7950 Flex Edition found here that comes with an HDMI to DisplayPort adapter if you want to and are able to go that route.
With the Flex cards you apparently can do Two DVI and 1 HDMI, all other 7870s and 7950s require the third display to run on DisplayPort. You can overclock on any card you buy, how far you get with overclocking will vary depending on how lucky you get on the quality of the chip on the card, and the effectiveness of your card's cooler.