Under point 1, a belief that some ethnic groups are less intelligent than cattle, but believing that it is not a negative trait, would not be racist? I'd classify that as a racist belief, wouldn't you?
Where would that subhuman line be? If they think an adult from one ethnic group is as intelligent as an infant in another, but that there's nothing wrong with that, is that believing they're subhuman and hence racist?
These things have no clear lines, welcome to reality.
This response applies to the previous line about being the intelligence of cattle as well, now that i've given it more thought.
Intelligence can be measured so more context would be needed here. In this hypothetical scenario has one group of humans either fallen through some kind of circumstance to a lower level of intelligence(not knowledge) or another has gained significantly more intelligence through some means? In that case they should probably be considered separate species not separate races so we're in a whole new ballgame.
Either way, when "humans" are potentially that different (there's no defensible claim today that any group of humans is significantly less intelligent than any other really) this issue gets very hairy.
Someone thinking that today would definitely be racist.