GOOD ENOUGH. “RuBisCo maximises the chance that a CO2 molecule rather than a molecule of the much more abundant oxygen reacts with the substrate, by grabbing the biphosphate molecule and twisting it The trade-off is that this twisting makes it hard for RuBisCo to release the end product-hence its slowness. Arguably, RuBisCo is not inefficient, it’s as good as it could get.”
http://answersinscience.org/EvolGreatestMistakes-NewSci%20081107.pdf