The 7x57 is good for most North American game and the 7mm has a little flatter trajectory over the 30 cal. Since you already have the dies, power, points etc. why complicate the relaoding process. Other options include the 7mm08, 280 or 7mm Rem Mag.
You didn't say how old your son was or what game you were hunting? If he is very young, that may rule out the 280 and 7Mag. On the other hand, if you will be making 300 yards shots that may rule out the 7mm08.