Must be a pretty expensive plate with only four characters on it. Mine is 5 with a suitably trimmed plate that follows the line of the bumper.
This is with legal spacing, legal height and legal font. Think it looks ok, so Go for it!!
Fancyplates will do you one cut down to an 11mm border, the minimum you are legally able to go to.
With a standard sized font, this is still noticeable smaller (especially on a short plate) so should look fine and not get you stopped!