how far can one turn down a crank?

bought a 340 duster in 92,..gave it mortal hell till 99, man i traded it to pulled motor and tore it down even tho it run great and found one rod journal turned .040! never could tell turning 7500 rpm erry day!! you could get that one journal repaired and turned back standerd but thats costly! i always felt all rod journals should be same size for balance but just my opinion...