hmmm, tough call. Brian (Sol93GT) is having great success with an HP kit on a bone stock motor (very low 11's with more left in it). The "problem" with the turbo kit is you'll soon reach the limit of the stock block. Once that happens, its gonna get expensive to go any faster.

With the 408, it may not be as streetable, but the blocks hold up better at higher HP. I'm thinking build the 408 now, spray it if you want, and when you get the itch to go faster a couple years from now, turbo that. Either way you won't go wrong.