Hi
You can generally get a 75 possibly a 90.rectangle for around the same price with much greater optons for equipment. Particularly lighting. With a 4/6 foot tank you can use "shop lights" can't give you the dims but a filled tank usually weighs 9/12 ponds per gallon get a strong stand no matter what you get lol gary

I had a 42 hex for years that was used for freshwater fish while in college and then as a marine aquarium afterwards. I agree wtih the previous poster. Don't go with the hex. They are prohibitive against lighting and filtration choices. Also, they tend to be deeper and don't have a lot of surface area to allow for good oxygen exchange. This can be mitigated by drilling the tank to allow for a sump (though again with the small base are you are pretty much limited to a remote sump), and by building an oversized canopy to house your lighting. All in all, not worth it IMO. After using the tank for 15+ years it is no longer in operation.

Regarding your question about sizes:

If my memory serves me correctly (and it usually doesn't), each side is roughly 24", and the overall height is somewhere between 25-28". Empty weight is probably around 30#. Water weighing approx. 8.35# per gallon would mean a total weight of about 380#.