I had this debate 2 years ago. I opted for the 408 build. Basically I got a really good 91 octane, 520+ crank hp for the cost of swapping a junkyard 5.7L (at that time). While that sounds cool, my 408 is pretty much tapped out on power. There's not much room to squeeze anymore power without deviating from pump gas. Unfortunately, that engine still had a carburetor (switching to Holley Sniper soon). From what I know, you can get a Gen III hemi to that power fairly easily and you can take it even further with power adders. If I were to do it again, I would have probably waited a little longer, saved some more money, and gone with the Hemi back then.