I get this question alot and the usda has an offical statement below.  Get yourself a good resturant quality thermometer.  It is quick and easy.  Just test and be safe.  Your food will be more moist since the higher internal temps just force out the moisture resulting in overcooked and dry meat.  Well unless beef jerky is your goal. 🙂

Cooking

Raw meat and poultry should always be cooked to a safe minimum internal temperature. When roasting meat and poultry, use an oven temperature no lower than 325 °F. Use a food thermometer to assure that meat and poultry have reached a safe minimum internal temperature.

  • Cook all raw beef, pork, lamb and veal steaks, chops, and roasts to a minimum internal temperature of 145 °F as measured with a food thermometer before removing meat from the heat source. For safety and quality, allow meat to rest for at least three minutes before carving or consuming. For reasons of personal preference, consumers may choose to cook meat to higher temperatures.
  • Cook all raw ground beef, pork, lamb, and veal to an internal temperature of 160 °F as measured with a food thermometer.
  • Cook all poultry to a safe minimum internal temperature of 165 °F as measured with a food thermometer.

http://www.fsis.usda.gov/Factsheets/How_Temperatures_Affect_Food/index.asp

http://blogs.usda.gov/2011/05/25/cooking-meat-check-the-new-recommended-temperatures/

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