For image editing you'll want the fastest and most processors you can afford. Just going from a 3-year-old MacBook Pro to a new one made an ENORMOUS difference to DH's photography work. Images come up in 5-10 seconds instead of 30 seconds or longer (each).

Another thing to consider is it depends on your internet connection, whether you need the optical drive or not. If we had to download a full version of Photoshop over our DSL because we didn't have an optical drive ... I can't even imagine. I have a couple of image-heavy anatomy apps on my iPad, like 700 MB each, and each one took all night to download. That's just a CD's worth, forget about a DVD or two.