Jakob Nielsen says that 0.1 second is about the limit for having the user feel that the system is reacting instantaneously, meaning that no special feedback is necessary except to display the result...
>>In gaming, delay of 100ms is huge enough for anyone besides the most casual players to notice.<<
I agree.
I used to play a drum beat game with my daughter and son-in-law, who are both professional musicians, and they could hit beats within a 10ms window, while I struggled to get under 100ms.
But 100ms seems like a reasonable upper limit for autocomplete to me.
PS: My son-in-law is a professional drummer and can't play Rush YYZ on Rock Band (just had to include this tidbit cause it'll piss him off)
https://www.nngroup.com/articles/response-times-3-important-...