News Gothic looks quite nice (though not as beautiful as on Adobe Typekit, but I guess that's due to different rendering techniques), but Source Sans Pro doesn't render that well here. Here's a screenshot, though it's slightly blurry, which is not how your text renders.

It's not very bad though. Helvetica is much worse on the web in a Windows environment. But if you look at the /R in Source Sans Pro, I don't think it's hinted properly. The bowl of /p and /b also renders too wide I think.

Rendering aside, the typefaces do work quite well together, but I'm not quite sure why it's important to have the same x-height here.

Hi Martin, thanks for your input. You're right. Source Sans looks awful in the image you linked to. Hm, wonder why. What browser? In my browsers on the Mac, the page has a far better look-and-feel. Regarding similar x-height, I think it creates a stronger feeling of kinship between the two faces. Maybe not a critical issue but I do think it matters.

I'm using Chrome, but it looks the same in other browsers. I think it has to do with the differences in rendering methods of text on Mac and Windows.

I think the x-height is relevant if you're going to use the typefaces at the same point size. Otherwise, I think the stronger feeling of kinship is mostly an appreciation of consistency and has no actual effect on the aesthetics. I might be wrong though.