Consider the trade off; a smallish bookshelf with a set of subs may cost about the same as a larger full range, and the full range, while taking up less room, perhaps, will likely be more coeherent across the entire spectrum.
I tried sub/monitor combos several times over the years and always returned to full range. I found that usually the midrange suffers the most due to the cabinet considerations and size of drivers. However, an exception was the much larger Wharfedale Opus 2-M2 monitor and matching subs. It is a much larger than usual "bookshelf" speaker, which was critical in competing well with its floor standing sibling. You can read it here:
http://dagogo.com/View-Article.asp?bShowUnpublished=&hArticle=759&PageOfArticle=1
I tried sub/monitor combos several times over the years and always returned to full range. I found that usually the midrange suffers the most due to the cabinet considerations and size of drivers. However, an exception was the much larger Wharfedale Opus 2-M2 monitor and matching subs. It is a much larger than usual "bookshelf" speaker, which was critical in competing well with its floor standing sibling. You can read it here:
http://dagogo.com/View-Article.asp?bShowUnpublished=&hArticle=759&PageOfArticle=1