Sask, if your in north america you own an is300 right,? Id get the stiffer bars as we dont have a 4-banger and ended up with the heavyweight of an i-6. The stiffer bars will help turn in, and flatter cornering asumming you get springs to suit the sway bar. So my suggeation is pick up a book from carrol smith called tune to win off amazon.com. anybody wanting to know true suspension engineering needs this book.