Run much faster than that. I use 1000rpm for nearly everything from 4mm up to 5/8"-18. I have found taps cut better at a good speed. The metal seems to flow easier and form a good chip. Lubrication is also important and I run mine at a 10 to 15% mix which gives better tap life.
Small taps in mild steel a sometimes a bit of a problem and I always try to sneak the drill size up a bit somewhere between 65% and 75% full thread. Repeat Rigid Tapping also helps. Go in about two threads, back out and then go four, then six until you reach your depth. Make sure Repeat Rigid Tapping is turned on in both places in the Settings/Parameters.