Properties of veg oils-cetane number is the one ur interested in,derv is 45 minnimum:
Vegetable oil yields, characteristics 2: Journey to Forever
Bio is always higher than derv,and a better lubricant,but contains less energy,so on the whole can expect slightly less mpg.Veg is also a better lubricant than derv,but you need to get a complete burn to deal with the glycerine component,otherwise carbon build up after extended use.
So overall,you should expect slightly less mpg on biofuels,but it does depend on individual circumstances