Fi Fi P on "Featured image"

I have continually found this a problem and no clean, simple answers.
For my site, I want all of my standard pages to display the featured image full width at the top of the page.

I have added the below code to my functions.php file:

if ( function_exists( 'add_theme_support' ) ) {
add_theme_support( 'band-top' );
set_post_thumbnail_size( 1000, 300, array( 'center', 'top' ) );
}

I then regenerated my thumbnails and on my page.php I have inserted the below where the image is to appear:

<?php
if ( has_post_thumbnail() ) {
the_post_thumbnail('band-top');
}

In my CSS, to keep it responsive:

#content-area img {
width: 100%;
}

My problem is the height of my image. I want it to be 300px high without distorting the image so all featured images will appear the same size and be cropped from the top.

Any help would be great!