Both bikes have engines that rev quicker or slower. The R1 has a short stroke which makes the engine rev QUICKER, The ZX has a slower revving engine. Now listen I'm not talking about actualy RPM's but the speed at which the engine operates and spools up. This is another advanteg the ZX has on its side due to its lower revving engine, and being able to start making power lower than the R1. Also this aids in the close ratio gearbox, it requires less effort to keep the bike in the power. The R1 would require 2 downshift to get the bike back up into its operting speed as to the ZX, because the R1 needs to rev higher in passing and etc. I hope this made some sense.