I have some pretty big mitts as well, and have tried a lot of different option. Mice like the Deathadder while being a bit bigger, are still way too narrow for my hands. I have ordered a Jumbo mouse as seen in an earlier post, and look forward to disco madness, but use a R.A.T. 7 setup that I really like. It is expanded out as far as it will go and then I have added about 3/8" of rigid foam to the right hand side, and it feels like a huge improvement. It makes the mouse about 3.25" wide. As opposed to 2.38" wide Mighty Mouse.
buttons and scroll wheel feel really good, and I could even do some gaming if I wanted.
My hand span is 10.75" (27 cm), and 9" from middle finger tip to crease at bottom of hand.