How many will a 1.7kg turkey breast feed?

there are MANY variables, not the least of which is the size of the breast. I have found approximately 6oz per breast is not an unrealistic estimate.

assuming your talking boneless breasts, that says you are getting just under 3 breasts per pound. so one could estimate 120 portions, but be sure to allow yourself some margin of error for those variables. bone on will of course be cheaper, but will lower the number of servings per pound.

good luck