Hi Andrew,
I find reading the spreadsheet adds 250-500ms.
Not a lot, but I have a lot of onEdit triggers, where this sort of delay is noticeable, so I try to keep spreadsheet reading/writing to an absolute minimum.
The cache service is sheet (or script) local, so couldn't be shared across multiple spreadsheets.
I guess I could read a remote sheet during my onopen trigger, and write the data to a local sheet (for any formula which use it) and to a script cache.
Would this be stable for many users opening the sheet while others are running functions or code?
Thanks,
Tony