I have two asians in 8 foot tanks that both started out in 6 ft 180s. In my humble and honest opinion, a 6 foot tank is not long enough although many keep them in smaller tanks. If you want them to have the room to bolt without smashing lids when they get spooked, and they do, 8 feet is ideal. My gold used to smash the lids when he spooked in the 6 footer and hasn't hit the lids since being in the 8 footer. He spooks occasionally but goes the length of the tank instead of vertical.
One tank is 8x3x24 and the other is 8x2x2.