My 300g (72"Lx36"Wx27"H) is mounted 42" off the ground. At this height, a step stool and tongs are a necessity to do basic maintenance. If the tank were any taller, given the overall width, it would be a real challenge.
If you will not have equal access to the front and back, I would not go any higher than the 28" you mentioned.
BTW, I love having the tank mounted higher up. When people come over, no one has to hunch over to look in.