I build 600+ HP small blocks, but not for street machines. A modern V-6 with multi-port injection and 4 valves per cylinder in stock configuration in a stovebolt would keep up with the average V-8 conversion, and still meet all the federal emission standards. The twin-cam I-6's will do the same, if not better because of midrange torque. A little reprogrammable chip tuning on any of those engines, and the Detriot iron is in deep doody! I love the sound and "geewhiz" factor of a big V-8, but getting reliable operation and 20+ MPG, plus tire smoke on demand is a pretty impressive thing, too.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!