There is a formula for calculating the maximum Constant Discharge Rate (in amps) of the cells required for a regulated mod.
Wattage / Cell cut-off voltage / number of cells / mod efficiency = max amp draw per cell
Most mods cut out at around 3.2 volts, but we can use 3 volts for safety. The cut-off voltage is when the most strain is put on the cell.
Most modern regulated mods have an efficiency (i.e. how much power reaches the atty after deducting the losses to the board) of at least 85%, so we use that figure, in the form 0.85
60/3/2/0.85 = 11.76 amps per cell.
So at 60 watts, on a dual cell mod, a pair of 30Q, HG2, VTC6, etc will be fine.