Header Logo size

Hi Amnion,
You can adjust this to your liking just by adjusting the CSS associated with the logo size, i.e. this in your style.css file that comes with the efficient theme:

style.css - Starting line 190

#header {
float: left;
width: 569px;
margin: 0;
padding: 0 0 15px;
}

#header h1 {
margin: 15px 0 0 25px;
}

#header h1 a {
display: block;
overflow: hidden;
width: 357px;
height: 88px;
background: url(images/logo.png) no-repeat;
text-indent: -10001em;
}

The width of the H1 logo is by default 357 wide by 88px in height. You'll have to widen this and toy around with the width and height if you want it to display across the whole shaded rectangle.