What you have now is probably enough as long as the stalks arnt streatching. But my main concern would be growth and color. You might want to look into getting some T5s or MH. I know when I switched to MH from PC my zoas looked and grew 10x better. I dont have T5s but have heard lots of great things about them.
Yea, It really isn't "wattage/gallon" that matters, more or less the type of lights and the intensity of them. Also important is the height of the tank, that would help determine what lights would be best as well... But usually T5's or MHs
I have a40g long with 220w of VHO super actinics and a 250w 14k Hamilton SE and I have some that have long stalks. I have placed them under directlighting and they still had the long stalks so I just moved them back to where I liked them. I wouldn't worry to much about it unless they are looking under a bit of stress.....