no, dont bother, especially if you have a 4x slot. Its not just losing 2-5 fps, it causes serious stuttering more so than if you had 2 8x slots. Ive been there and done that with 6850's and am selling them to replace them with a 7870 or gtx660. I have sold one already and games are smooth again even with a single card, lower fps, but smooth. I suggest you sell it, and put all that money to a better single card. not to mention the newer cards have 2gb vram which will help in some newer titles.
Currently I only use 1 1080p monitor to game with so I don't even know if I need more than 1 gig of vram in the first place? I keep hearing mixed reviews on crossfire x that its good and bad for this card. hmmm.