I've been keeping my Gatf in a 2 feet wide for a year and it's way overdue for an upgrade which I'm building for September. 3.1 is good until they are around 24-28" and then they are dying for another upgrade. If you want a giant gatf, Id recommend no less than 5ft width which is what I am going for on my new tank. Width and foot print is the most important. I think the size you are building is a decent size for vatf and other ATF species for life and if you don't mind gatf growing to their potential, I guess they work too. I have seen many ATF raised in tanks way too small for them and still grow to an impressive size and stay quite idle and feed healthy. Obviously it's not good for their health in a small tank and I'm not advocating for that but ive seen it all too often here in asia. Its also here that you find 4 ft GATFs as well in giant swimming pool sized tanks. So take it with a grain of salt in this hobby, as long as you provide the best care for them and happy.