GO EXTREME! ! ! LIQUID NITROGEN CPU COOLING OVERCLOCK IT TO 6.5 GHZ! ! I'm just kidding but really 4.2 Ghz would definitely be fine and if you wanted to go higher just inch your way up testing it as you go ^_^
if you can keep it cool and your volts under control, sure, why not. if you have to run too hot or with too high of volts, probably not worth it.
i mean, itll perform better. do you really need that performance? probably not, at least not yet. when your computer gets closer to its end of life though you might want every bit of performance you can get.
personally i just like getting as much performance as possible without spending buttloads of money
edit: i actually prefer sandybridge over ivybridge, because sandybridge overclocks better.