We use 6.4 but will upgrade to 6.5. No information on PE website about the difference between versions.
Just like you, I have searched differences regarding the 6.4 and 6.5 versions, but there aren't any available. The official website, doesn't provide any information at all. The only way you could obtain the details about the versions released is through the developer.
Use the following website to access the contact options: http://www.perkinelmer.com/corporate/locations/