Oh nice, I had never considered that! Thanks for this new conclusion that flows naturally from two of my beliefs: Brain size differences between species don't correlate strongly with intelligence differences*, and suffering is bad.

*It's mostly brain-to-body mass ratio that seems to correlate.
http://en.wikipedia.org/wiki/Brain-to-body_mass_ratio
Within 1 species, there seems to be correlation.
http://en.wikipedia.org/wiki/Brain_size#Intelligence