Taking the seat out actually increases the movement of the shell under cornering. Put a brace in if you decide to take the seats out and/or adjust the tyre pressures to compensate.
i removed the rear seat install and it made absolutely do difference on take off or power at all, but made the back end uneasy round corners so i put it back in that night.
I took mine out 4a few weeks while I was cleaning them. No differance of handling or speed. Yes it wud make it quicker, but it will not be noticable unless if you run 1/4miles and then it may be like around 0.07 of a second quicker.