SIZE DOES NOT MATTER. “It is not clear that the ∼12,500 genes of Dictyostelium discoideum or any of its eukaryote-specific cell structures give it an advantage over Myxococcus xanthus, with ∼7,500 genes (and no eukaryotic cell structures).”
http://www.pnas.org/content/112/33/10278.full