the norm for Nismo injectors. With any load latency barely effects my a/f values. If I am to go into Nistune and change latency from say 790 to 850 my idle will go go about .5 a/f richer (off the top of my head...haven't done that in awhile + I'm running shitty DW injectors so results may vary).
Moral of the story is if the only difference between the tunes is latency, pick the tune that gives you a smoother idle.