I used the nutritional data sheet supplied by GPC for m580. 100g contains 376 cal. I think the difference is in density. On my gram scale it takes 3/4 cup of m580 to equal 100g. Measuring cups also vary in accuracy so my calculations only appy to my measuring cups.

m500 is less dense .34g/cc compared to .40g/cc for the m580 (according to the GPC website)

The key thing is once you have your basic ingredients you are in total control of the recipe and will need to discover during your training what works best for you. Do not experiment on race day.