Good 1/0 is rated around 300 to 325 amps over a 50 foot run.Shorten that to 15 foot or so,and the capacity goes up. The way I look at it... If your alt can only produce 250 amps +/- ,and your "single 1/0" can easily carry that amount of current...what good does it do to have that much excess capacity?
I run a 320 alt,and 6 batteries in back feeding 2 5k's,and a pair of 4 channels. For quite a while I ran one run of 1/0 with no issues.Then one day I had a bunch of extra 1/0 laying around ,and ran a second run.Did it out of curiosity,just to see if it would help anything.Nothing noticable came out of it,maybe .1 volt.MLSTRASS did the same thing a few years ago.If I remember correctly he went from one run of 1/0 to 4 runs of 1/0 and gained .1 volts as well .
Whether it is money,space,or plain do not care...try one run for yourself just to see.Extra battery in back would probably be a good idea though