Yes it would. Here is the review, OH and I say this because I have one personally.
"Since the Radeon HD 5850 is cheaper, it automatically becomes more appealing just by price alone compared to the Radeon HD 5870. However, when it comes to Eyefinity resolutions there can be big differences between the HD 5850 and the HD 5870. DiRT 2 is a good example, in this game we were able to run with all the new fancy DX11 Tessellation effects at 5760x1200 on the Radeon HD 5870, but we were not able to with the Radeon HD 5850. The Radeon HD 5850 is the video card where we would call the edge of what you want to be running with Eyefinity resolutions."
Your only running two monitors so yeah. The 5850 is enough.