You don't want to do that.
Because biggest body to brain ratio is in birds.
We come in second.
The bird's brain is mostly devoted to sharp, color sensitive vision. It apparently takes a lot of wetware to make that work. It is possible the Neanderthal brain size was for the same thing. Their eyes, were based on the averages of the remains we have found, larger then Sapiens. Tetrachromacy had to come from some where.
A meaningless example. Bird mass is low because it is designed (or evolved, doesn’t matter here) to fly. So any ratio is flawed.
Comparing a whale to a biped is poor enough, but at least they are both mammals.
Comparing two biped apes with 99+% dna overlap and the same basic niche is a fair bet.