I don't know what's best for the showring but our commercial calves we cut at birth (never had any problems with a couple hundred a year). Our neighbor cuts his at 5 or 6 months and every once in a while, one will bleed to death (it's not very often but it has happened to them anyhow). Commercially speaking some like to leave them bulls for the extra growth, but all the grid data and articles that I've read has always said that calves cut at birth grade better on the grid (but if your not selling on the grid I guess that would not matter).