Anything over 2000 rpms is probably a safe bet w/o bogging it. Or just listen to the engine and experiement a little. Shift low and see at what point the engine bogs (which is detrimental). My Mazda didn't come with a tach, so I'm used to just listening when to shift. Keep your eyes on the road, not the tach!
A lot of 4 cylinders are designed to be revved high, that's where their power band is. In comparison to an 8 cylinder which generally has much lower end torque and redlines around maybe 5000 rpms which is where a 4-banger comes alive.
And I drive my n/t Laser with a 4g63 pretty hard, revving around 4500k regularly. Even then, I can crank out a minimum of 350 miles from a tank.