Now, Google's John Mueller said outright, that using uppercase or capital letters in your URLs has no ranking impact in Google.
The question asked in the Google Webmaster Help forums was "I want to know capital letter in our web URL impact our SEO performance and ranking."
John Mueller responded quiet simply "nope," and former Googlers Pedro Dias also said "no." So I think the answer is no, capital URLs has no impact on Google's rankings.
It is a topic we covered several times, but it is a slow week and Google mentioned it, so why not cover it again.
Forum discussion at Google Webmaster Help.