Answer:
The USDA has a ground beef calculator for this question. The calculator reports the technically correct, "kilo-calories," which is what food labels list as "calories". It can take an input of 5% to 30% fat meat. I got these results using it:
5% fat meat is 621 calories per pound
10% fat meat is 798 calories per pound
15% fat meat is 975 calories per pound
20% fat meat is 1152 calories per pound
25% fat meat is 1329 calories per pound
30% fat meat is 1506 calories per pound