Submit seo services company has given good though on this issue. Either we should use capital letter or small letter or the first character of each word with capital letter in keyword phrase.
and it is well said that small text linked as anchor text is part of natural link building plan. question I though is why Google giving difference in search results for various way of writing a word with same alphabetic
http://blog.submitshop.com/2010/06/23/use-of-small-or-capital-letter-in-anchor-text-link-building/