Unless there is something wrong with the 1.0 you downloaded, there is no way in hell it is lagging with 80 players unless:
1. Some script was done wrong and is doing crazy things in the background (this does not always provide an error it could be something looping over time)
2. Something you added to the source that was done wrong. (again not always going to provide an error)
3. You downloaded it at a bad time when something added was unstable and not fixed yet. (idk if that has even happened since I don't follow the project much)
4. The server is not lagging at all but in fact it is ddos. (sadly enough this is the most likely scenario)
Next time it lags check the servers cpu/memory usage. If all seems normal check your email, OVH often notifies you when your server is under attack.
Edit:
I almost forgot to add... make sure anything you allow the player to control (!commands/actions/ect..) that involve database queries have an exhaustion. People like to exploit these types of things to bog down servers.
Some common examples would be !frags/redskull remover/!shop/!deathlist
P.S.
@narko
An SSD would be way overkill for an OT server since most of everything is just pulled into ram anyway. The only thing it would speed up is the logging in/out of players/bootup/server saves/ect. Also gl finding an affordable hosting solution that offers SSDs currently, and by affordable I mean "realistic" for someone hosting an OT server.
Although I don't use it for hosting OT, and when I do, its for smaller custom maps that don't require much ram. (<2GB).