Let the figures do the talking...
http://www.redbookasiapacific.com/au...L&key=HOLD03LJ
You just got to make up your mind... do you want fuel economy or not
Either way you'll need another engine...unless you go aftermarket supercharger.
Not alot of difference between motors from 0-100...
I think you'll find a super6 would probably be the cheaper solution...same engine mounts, same front suspension, same brakes. Dropping in a V8 would require alot of work, new exhaust, brakes, suspension, roadworthy testing...etc...etc
You may aswell take the 10 G loss and go buy a v8 by the time you're through...