[SV0L0CH]

Как быстрее?

Быстрее так:

function cond(string) {
    return string.indexOf("undefined") == -1;
}
var a = [];
a.push = function(){
  return [].push.apply(this, [].filter.call(arguments, cond));
}
a.unshift = function(){
  return [].unshift.apply(this, [].filter.call(arguments, cond));
}
a.push("82undefined", "82undefined", "822025", "822025", "5undefined2775", "83232");
alert(JSON.stringify(a));
a.unshift("82undefined", "82undefined", "822025", "822025", "5undefined2775", "83232");
alert(JSON.stringify(a));