You should keep the revs down until the oil warms up, not just the water temp!
The temp guage on the dash is only the water temperature and heats up quite quickly, the oil takes much longer to heat up and you're engine is not protected until the oil is fully up to temp!
Fit an oil temp guage and keep the revs below 3k until you get some movement on the guage, then keep below 4k until fully up to temperature. Oil pressure guage is also useful to see how viscous the oil is - when cold, the pressure stays high when you change gear, the warmer the oil is, the more the pressure will drop between gear changes.
Without guages to help, typical warm up times are around 15 minutes in the winter and 10 minutes in the summer.