Goku can adapt to basically any trick used against him and develop a technique to counter it. Teleportation, Solar Flare, Zanzoken which works against people who can sense ki, everything in his arsenal would become twice as much of a problem with a 2x gap. Goku has beaten people with great analytical prediction before, even people with his own level of it. The enhanced senses only help if he has time to react, and in close quarters? I'm not sure that's possible.
Also, Goku could use instant transmission Kamehameha, which dwarfs his own level of speed and reactions.
I'm talking about hand to hand combat exclusively. In terms of Taijutsu alone, Goku should have an advantage. Couple that with a x2 speed amp, and Goku is not getting hit.