The reason Tobi can use his MS Sharingan without any damaging affect is because he have the first Hokage cells, so he don't need to implant new eye's, so Tobi need to just shut up with the trash talking to Kakashi who not even a Uchiha, but a top 6 best sharingan user problemly in Uchiha history. That why Sasuke & Kakashi need to get some of those golden first Hokage cells and that also the reason why Tobi being Obito will make him overrated and the worse villian ever.
If Sasuke, Itachi, Madara, Izuna, Shisui grew up with Kakashi, they would of been better or atleast on par with Kakashi as young boy's, but Obito was nothing before awaking the Sharingan and after at best a average young Uchiha ninja. If Tobi turn out to be Obito(which he have to have some connection to Obito now because Kakashi and Tobi have the same MS design) now he will be way better than Kakashi, had Itachi clueless and had fourth Hokage worry in a big fight. These are three of the smartest, most talented ninja in Naruto manga. It will be just to many hole to fill for me to buy Obito (from what we seen of him), as this underdog ninja who now the top villian of all time so far in the manga. That is to big of a jump for a incompotent young ninja, maybe he is evil Naruto.