PMI just released a 70/4500 HP paintball n2 tank.  70 cubic inch tanks are designed to be shorter and fatter than the standard 68 cubic inch size.  The advantage is you can tuck the gun up closer to you.  The PMI 70/4500 comes from the factory as a high pressure tank (800PSI output), however a Low Pressure conversion kit is also included in the box, which makes this a great deal.  The 70, like all other 70 tanks are love it or leave it.  It has no real advantage over a 68ci tank other than the “peanut” shape.