First, testing for top end speed should be done alone to keep weight consistent. If you were getting 76-77mph with two and tournament loads, those number should be obtainable by yourself.
Biggest difference, a loss of 500 RPMs with the Fury.
For more input, post this issue on BBC, Mercury forum, have your engine serial number stated in your post.
http://www.bbcboards.net/forumdisplay.php?f=7
Don