Question about an 800A load and how many 1/0 cables required?

I am having a brain dead day today and just cannot agree with myself on what sort of cable system I will need for this pump. The maximum draw for the pump is ~800A and it is powered by a 480VAC 3-phase source. Voltage drop is negligible because we are talking 20feet max. Considering the equipment we have on hand, 1/0 cable would be preferred because of the cost savings. I have a guy telling me that four 1/0cables per phase (in conduit) will have the ampacity to accomplish this. I know that the NEC requires the ampacity to be derated to 80% of its value with four conductors in one conduit so I am thinking more along the lines of biting the bullet and using three 350MCM conductors per phase. Can anyone bring some fresh eyes to this and let me know if I am thinking correctly? Thanks!