I'm going with McClellan by ko here because while Griffith was the far better boxer he was past his best at Middleweight. Thoughts?
You have a good chance to be right because when McClellan fought as a "middleweight " he was entering the ring at 180 or more, which would have made him a heavyweight at the time that Griffith was a middleweight.
The Gman can lose Emile Griffth was great, however a cruder smaller less powerful weaker slower slugger in Rubin knocked Emile out.
I like Griffith on points. McClellans resume was wafer thin compared to a well rounded, highly durable pro like Griffith. The total lack of defence and one dimensional game plan of McClellan would be exposed by a technician like Griffith who was perfectly comfortable winning boring and ugly.