You know Matthew, you can just use the one larger image and apply a width size to it, thus changing its viewing size without having multiple images. Whether directly injecting via img or by use of a class and css.
Logo's are obtrusive IMHO, unless specifically for larger scale operations where branding outweighs all else. Site names can be done in so many ways... change to vertical text up the side of an existing container, thus space is not being wasted horizontally with large spaces to the right or left due to a logo being in place.
I would suggest to take a look around at some creative designs and how they incorporate logos into their sites. There really are quite a lot of excellent ways to do it.
A new design I'm working on now will show the logo to guests on a bar that is stripped of content to members and replaced with member relevant data, as members don't need your logo wasting space as you have converted them into a member. However, one can then use subtle branding to include the site name elsewhere, ie. as a feature look to say the user block in posts.