I am planning on buying a new iMac but cannot decide between the 21" or the 27". I am an attorney so I'll be using it mainly with MS Office, i.e. Word, PowerPoint etc. Drafting documents, email and research are the main uses. I love the 27" but with the screen that large is it overkill? I really don't want to spend the extra money if there's not much advantage given the limited use.