You will not get 220W from 2 tubes at all. My 4 bulbs give out only 120W. Hopefully tomorrow i'm buying a 150W metal halide and i'll use the 2 t5's.
Anyways back to topic, from 2 tubes you might get around the 50-60W mark, but no more. Specially if they are T8's you might get even less.
T8's are fatter tubes, and T5's are slimmer but much better and brighter, just in case you dont know.