I don't think it would make any difference. I've gone over 1,000 events in my project, though it is down below 900 now after removing some stuff. Of course, it'll probably be back above 1k when I finish.
I don't see any reason to spread them across multiple event sheets unless you want to for organization. It'll still be the same number of events.
I like one big sheet with things put in groups because it is easier for me to maintain than jumping back and forth between a dozen event sheets.
If spreading it across multiple event sheets makes it easier for you to manage performance (like you said with including event sheets per layout) then do it.
All that matters is how many events are active and how many are affecting performance. Whether you do that with everything in one event sheet or spread across multiple ones doesn't seem to make any difference to me. Be more concerned with the total number of events that are eating away at your resources and need to be optimized. Groups can be enabled/disabled within an event sheet, and there are sometimes better ways to write your events to be more efficient.