Hmm, I've read that carbonation (such as in Coke or beer) makes the alcohol absorb faster into your bloodstream.
So a stiff Jack & Coke should hit you harder than drinking the same amount of Jack by itself in the same amount of time.
Edit - found this...
"Once alcohol is swallowed, it is not digested like food. Instead,
a small amount is absorbed directly by the mucosal lining of the mouth. Once in the stomach, alcohol is absorbed directly into your blood stream through the tissue lining the stomach and small intestine. Food, water and fruit juice help to slow this absorption,
while carbonation works to speed absorption."
From -
http://www.runet.edu/~kcastleb/steps.html