Which will go first, LED or Uno?
The Uno.
When a LED is slightly over driven the light output reduces at a much faster rate than normal so its half life is shortened. That is the time it takes for the light output to drop by half. So no instant smoke.
Have you seen what you can get out of a Uno pin:-
http://www.thebox.myzen.co.uk/Tutorial/LEDs.html
Taking more current than the rated current from a pin is just like taking crack, it won't kill you at first but it sure messes up your insides. Do it for long enough and it will kill you.