I personally use one bridge, so 'need' is one 'want' would be two in my book (or to squeeze a frame or two for E-peen)
**temps fine as mentioned, top card usually see's penalties heatwise, options for controlling that are Watercool them, aftermarket coolers, or modding some additional fans to give the top card sufficient cooler air (Something one member has done in the gallery)
As you can tell there are still people saying two bridges for xfire ,So to clear this up i talked to the techs @ XFX and there answer was one for xfire and two for trifire.thanku for all your replies,but the answer is 1......
You only need one to use Crossfire. With my two 6870's I used one bridge. My buddy loaned me his bridge because he wasn't using it and I got an extra 3-5 frames. I remove the bridge I loose the frames.