I'm not disputing that you can detect latency on these mice. I gave it the best, fairest shot I could and couldn't find any myself, but it's pointless to argue over what someone else perceives. What I felt on the Spawn I didn't feel on the G400s, so either the G400s has lower latency or (more likely) the shell just fit better for me to flick with.
What bothers me is that 'smoothing' now apparently causes problems such as inconsistent CPI when the mouse is moved in different directions, which is downright silly. Also not actually your fault but that of people with poor reading comprehension, but whatever.