Big glass tanks are not really popular and the majority of folks seem to go with acrylic when they start to get to be in the 300g category. Personally I like glass tanks and am looking to get one from customaquariums.com. They have a 96x24x30 tank that I want and I have the option for low iron clear glass on the front and sides. This is what I am going to do.
jaws, I think you are on the right path to just skip the middle step and go to the 300g. I did the step from a 120g to a 210g and now I want the 300g. You going from the 150g to a 300g is a good step, saves you money in the end.