Exactly, its speculation, current estimates do have it at a similar size to average T.Rexes, BUT, that's just one specimen, larger specimens maybe even as Large as Rexes like Scotty, maybe even bigger, we just don't know yet...
SO, Mcraeensis for now maybe unlikely to be 100% slightly bigger then T.Rex, but with future fossil discoveries, studies and descriptions of T.Mcraeensis, them we maybe able to 100% know if Mcraeensis was slightly smaller, the same size, or bigger then T.Rex