RE: 708 vs. 308
Both the 7mm08 and 308 are great cartridges. The 7mm08 is probably slightly flatter shooting, but realistically I doubt you will notice much difference in the field. Either one will kill anything that walks in North America with the proper bullet.
I would probably choose the 7mm08, since I have a 30-06 and dont own a 7mm of any type.