Im a huge straight 6 fan, we have a car here called the Ford Falcon which started life as a 144ci engine in the 60's, it has been modified and evolved by ford over the years and now the engine is 4lt and churning out 261 hp and 288 lb·ft in its factory base model form. Tuning companys have modified it to produce 1000hp and 740 lbft at 3500rpm (7200rpm redline) with a stock head excluding cams a valve springs.
If this isnt proof that the straight 6 is a formidible engine i dont know what will