"Calling a Baptist 'Reformed' is like calling a Presbyterian 'Baptist' because they believe in believer's baptism."1
I think Clark has a good point. One should be cautious and deliberate in how one applies labels. To do so flippantly can result in a misrepresentation. With that said, is it a misnomer to call a Baptist Reformed? I argue no. Simply, it seems as though a Reformed Baptist would argue that they are indeed Baptist, but, more specifically, they are Baptist with theologically Reformed leanings. More to the point, it seems as though Reformed Baptists would argue that they are Baptists who affirm the five Solas of the Reformation and the five points of Calvinism.
Thus, it seems to me that "Reformed Baptist" is a fair category, and the label is proper. It also seems to me like this discussion (this blog post included) as to whether Reformed Baptists is a proper category is about as important as punctuation. Just because one is a reformed Baptist doesn't mean that they must hold to a paedobaptism. It is simply a more definite category of one's theological leanings. However, I admit, I make these remarks in a setting where religious liberty is a reality. Marpeck might have a different opinion.
1. Clark's comment can be found on his blog: http://heidelblog.wordpress.com in the post on June 6, 2009.