Any idea mate what a safe overclock would be for it?
Probably high 3 GHz range to mid 4 GHz. In reality you can't say because every chip is different. One person might be able to overclock it to 4.1 GHz and someone else might get it to 3.9 GHz. There are alot of things that play a role in how far you can overclock a CPU.
Room and enviroment temps especially now in the summer time
Cooling and type of cooler (a cheap aftermarket cooler vs a high-end cooler or water cooling)
and just the chip itself. After a certain point it just becomes luck on how much further you can overclock.