The 6.4 SRT cam is over $100 less than the 5.7 cam. The 5.7 springs are a couple hundred cheaper and seem to work ok and have similar spring pressure so I don't know what the difference is but I would get the 6.4 springs if I could swing em. The 5.7 springs do break occasionally after about 150,000 miles thats why I recommend replacing them while you have it apart.