Vitiate's Real Body Speculation

Well first of all we know that the ritual made him immortal and boosted his power. The question is: to what extent?

I'd say that in terms of immortality Vitiate's real body will not die of old age or dark side degradation, however I feel that this applies only to his real body and his voice is not protected from either of these things. Vitiate's real body however can be killed (though I think this would be difficult and will elaborate further on in my post), as this is the reason his voices serve as a conduit for his spirit rather than Vitiate conducting his business in his true body despite it being a superior conduit (again I will elaborate further on in this post), as well as the fact that Vitiate died at some point before the events of Darth Plagueis.

The other main effect of the ritual is that it boosted his power. I don't think he wielded the entire combined power of 9,000 Sith Lords and Nathema however, as a good deal of that power went towards granting him immortality, and as power taken from others isn't usually permanent, it's a safe bet that another large amount of this power was forfeit in order to solidify the power boost he did gain. In other words, rather than temporarily wielding the combined power of 9,000 Sith Lords, he instead wielded less than that amount of power, but wielded it permanently. If Vitiate had wielded the combined power of 9,000 Sith, he would be a hell of a lot more impressive than we've seen him to be.

The ritual appears to have had some very interesting effects on Vitiate's body. First of all there's the fact that Vitiate used essence transfer to travel between voices. What I found interesting about this is that essence transfer disintegrates your body as soon as you leave it for another body, however his true body survived and is still available for usage. His true body is obviously immune to this effect of essence transfer. His true body is apparently immune to the effects of Nathema due to the ritual of Nathema, as he was on it right after it's devastation and somehow got off of said planet. As his true body is immune to these effects I find it also extremely likely that he is immune to the effects of force drain as well, though not because he knows the technique but because of the effects of the ritual. As such it's also extremely likely that his real body can handle his own force power and the force attacks of others incredibly well. It's also likely that his real body is also more resistant to damage as a result of the ritual.

With all of this in mind I think Vitiate's true body as a conduit for his spirit and power is superior to any of his voices given how well it can handle the force and how it is less effected by dark side degradation meaning Vitiate could utilize his power more efficiently than he would in a lesser body. I also believe that Vitiate's true body was the one on board his space station, and all of this would explain why Vitiate's curbstomp on his space station was more impressive then his relatively pathetic defeat on Dromuund Kaas.

Well this is just my speculative opinion, but I think it's a pretty damn good one.

I fully agree. This would also explain how HoT managed to kill Vitiate where Revan failed utterly. HoT may be a bit more powerful than Revan but their confrontations with the Emperor are way too different and inaccurate. 

Also he wouldn't be able to dominate so many sith for centuries with the vulnerability of the Voice.