You can break past 100%, even! Trainsawlaser was at something like 130% last I knew.
The number you have to worry about is your in-game entity count, which you can find by loading your map up and typing in report_entities in the console. The number at the bottom is what you have to watch out for.
2048 is the max a server can handle before crashing, HOWEVER, each player counts as one entity as well as each cosmetic they are wearing, each rocket/ pipe/ needle they have out/ in the air, and a bunch of other odds and ends. I generally try to stay under
1400 entities active on the map before players. Pipeline is Valve's most entity heavy map and it's somewhere right around there.
Trainsawlaser's, for reference: