Alternatively remove the right sidebar. Greater width would be much more ergonomic.
On which pages of the forum? I mean I wouldn’t want to remove the sidebar of the entry page.
The content block (i.e. the white area) is 980px which is considered the max you can reasonably use if you want to avoid horizontal scrolling with a general audience. We could claim that we don’t have a general audience though and push this block out a bit.
I don’t think it’s going to be possible to have a fluid layout (i.e. using the full width) with the customisation options we have. We could use more width or remove the sidebar though.
I’ve pushed things out as much as possible without severe restructuring.