On the Perfomance Cat Website you get the same description by clicking on either 5.8 or 580. It just like the 5.0 = 500 and the 5.7= 570. I am sure there are subtle changes, but the Hull shape has remained unchanged . It is just not as popular a boat as when I used to race them in the middle 80's. In the 90's sometime NACRA/Performance did some updates and changed the names .
BTW: Nice website it has Zero info about either the 5.8 or 580!!