Figured in kilowatts it is bigger.  I did the math with a 240v delta service as that is what I have, but if you went with a 208v I guess it would the same as the 600 amp single.  

600 amps x 240 volts single phase = 144000 watts = 144kw

400 amps x 240 volts x 1.73(due to three phase) = 166080 watts = 166kw

400 amps x 208 volts x 1.73 = 143936 = 144kw

Yes it would be bigger in amps, but true power (watts) that can be turned into work will be more with the smaller 3 phase service.  


We have had a 240 delta 3 phase service for as long as we have had 3 phase.  I redid it in 2011 and they changed the transformers.  I had the option to go to 208, but chose to stick with the 240 for the higher voltage with 240 single phase loads.  Yes, it requires a competent person to make sure that the wild never ends up on a 110v circuit, but I think the voltage advantages outweigh the extra precautions.