well...go look at the ratios listed above. the 6th gear ratio is less than 1.0 so yess it is an overdrive gear.

BTW the only reason the 6 spd has a higher top speed potential is because of the fianl drive that was listed with the trans in that gear ratio listing. the 5th on a 5 spd adn the 6th on a 6sp are nearly identical gears. so the 6spd alone will not give your car a higher top end. you need to change rear end gear instead.