Expanding header image

[Taurus]

I want to exapand header image across the top of the entire template(default is from 635px). Layout example (http://demo.ifyn.com/). This template is very sensitive to the elements width changes

default css:

#header {
float: left;
padding: 0px;
margin-right: 2px;
width: 635px;
height: 150px;
background: url(../images/header_short.jpg) no-repeat;
}

Is it better to set image width 802px (635 +165 + 2px) or 800px?

#header {
position: relative;
float: left;
padding: 0px;
width: 802px;
height: 150px;
background: url(../images/header.png) no-repeat;
}