The 6 cylinder has better torque so it'll pull away from stoplights better than the VTEC 4 or VVTi 4. The VTEC doesn't really start pulling strongly until 4800RPM so if you want to win any drag races, you better be ready to fry the clutch. The Celica's VVTi has a very narrow powerband and so you have keep the engine within this powerband in order to get maximum power. Below 4000RPM, the Celica GTS doesn't feel any stronger than the Celica GT. I've had a chance to drive all these cars and I'll take the IS300's smooth and torquey engine over the other two any day.