You could hit shift-command-r while on a page to go to Safari Reader mode. That strips out everything but the article and fills more of the page.
If you are using a trackpad or Magic Trackpad, simply pinching outward will make the content larger, in a very smooth and intuitive way. I use this all the time.
Does Cmd + (zooming) help at all?So this screen is huge. Is there a way to avoid white columns and make the page utilize the whole screen?