I suppose another consideration is whether you (carrielsal) ever plan to move to steel tanks. If so, you'll want that extra lift.
John....... I love my Zeagle #55 wing, had no problems using it for single tank diving either! I much prefer a #55 over a smaller unit,,,,, now that I am diving doubles only plus all the other tanks and gear you have to carry on some dives! Course each diver must be comfy with what works best for them as you would agree. Your instructor is your first level of advise,,,,,the rest of us are just chatter-LOL . Several of us are trully trying to add good input to consider. Best of luck and you will find that solution 'in time'.