Obviously, someone with a shifter and manual clutch is slower on braking points and that is because your right foot has to be lifted off completely from the accelerator and press the brake pedal while in auto clutch the brake pedal can be pressed with your left foot while your right foot is still pressing the throttle. That's about one tenth in each braking required corner and let's say the track has five of them so you are already half a second behind. That does not apply when you use auto clutch and h-pattern shifter imo. Anyway, I even find auto clutch as a disadvantage when button clutch comes into play, for example pecholobo's hotlaps. Shifting with a button clutch gives you about two tenths on a straightaway compared to an auto clutch and better stability/control of the car at some corners (the last one is my opinion).