I don't think you'll honestly agonize over not having low-iron once it's up and running. I wouldn't sweat it at all. It's a "nice to have" but I don't think it's worth being a deal breaker. I would consider things like having the right overflow for what you want (e.g, two holes versus one if you want a Herbie overflow - coast to coast versus corner, internal versus external, etc.), the size and shape of the tank, and the type of bracing to be far more important considerations. And May versus August ... that too is no-brainer.
Also, I think water clarity has a bigger contribution to how clean a tank will look.
Glass just gets dirty and needs to be cleaned.
Oh, and I think low-iron glass scratches easier.
Hope that makes you feel a little better.
