The nominal weights seem to be identical between John's R28 SL4 versus R28 SL5. The only difference seems to be in spokes 2.0-1.8mm versus 2.0-1.5mm.
Based on the information on the Sapim website, it seems as if the 2.0-1.8mm spokes on the SL4 is more DURABLE than the 2.0-1.5mm spokes on the SL5.
Given that the weight difference between wheelsets is negligible does anyone know why the SL5 is better? Is there some slight aero advantage?