Regarding Johnsons true weight.
Looking at the weigh-ins against Arlovski we can say that Rumble is not a true HW and to be perfectly honest he didn't really look like a huge LHW either.
205lbs is a great weight for him, however i have a feeling that if we see him back in the UFC he may cut to 185lbs if it doesn't start well for him.
205 seems to be a good weight for him, at 185 he had trouble making weight and had to do a catch weight at 197 against Belfort and 195 in his following fight, because he couldn't get down to the MW limit. He walks around 235lbs