the 325i will most likely win, it has about 189 horsepower but is much lighter than the regal. A regal ls is a bigger engine with 200 horsepower but it is much heavier. Also the bmw offers a manual transmission while the buick doesn't which also fares well for the bmw. If it was a buick gs though it would be a different story because the gs' are supercharged six cylinders.