here's some recent research that shows what you eat has a lot more impact that how far it travels. all the water consumed and the methane produced in the production of red meat make it by far the worst choice you can make. methane is 25 times more potent as a greenhouse gas than CO2!
article:
WorldChanging: Cows Aren't Part of a Climate-Healthy Diet, Study Says
study itself:
Food-Miles and the Relative Climate Impacts of Food Choices in the United States