It's probably fine to feed them those. I'm not sure if you are questioning whether or not they are too big for your Savannah's, but if you are, your monitors will shred them into a usable size if they are too large.
If you ration their food, your monitors will grow slowly. I would suggest feeding them as much as they will eat while young since they have a lot of growing to do(but I don't think feeding them less is going to harm them unless they are starving). If they become obese, there is probably something wrong with your setup.
I would try to vary the diet as much as possible with crickets and roaches, provided your monitors will eat them.