With Metal Sonic... he is not faster than normal Sonic, so, np.
doing it fast is hard because the camera, always turn to somewhere that have nothing, and who play and love this game know how have a lot of bugs inside sonic DX.
I was killed by one glitch, close to the end, after a spin dash i was launched to outside of scenario, I lost a lot of time trying to fight against camera and using checkpoint, but I made a good time anyway. well, there is a total breakable record, i can do better... but i think someone will do it before haha