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No experience, but these look nice
http://midwestme.com/pages/productinfo.html
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I have been lopping off levers so as to be 2 finger (like my MTB levers), but that decreases lever arm and thus increases force. These adjust the pivot arm to reduce that force.

I've got these levers on my 450 EXC clutch and they work great. I'm not sure of the physics, shorter but much easier to pull, but I can vouch for the fact that they do work. If I remember correctly, kind of expensive, but worth it.