Your thermostat is probably a 195, so it should run at about 195 - 200 or so at the most under normal conditions. I'm not sure what a safe temp is that it could go up to. But if it gets up to high you could blow a headgasket easily. I would say to shut it down or turn your heater on if it ever starts getting up past 225-230 or so. If it gets that high you probably have a clogged radiator or a bad clutch fan.
Its hard for me to say exact temps because the only truck I have a good temp gauge in is my race truck and I don't have a thermostat in it, just a washer. So just driving around on the street it only gets to about 175-185 and under race condiditons its probably at 190-200.