Four Meter cables are about 13 feet. That's relatively short, so I don't see a problem. Though a reasonable effort should be made to keep them away from power cables.
Input cables must be shielded because the signal level is very small, so any microscopic signal induced from power cables will produce hum that will be then amplified by the amps. However, speaker cables are high signal level and the hum picked up by the cables will not be amplified, so it is generally not a problem.
If you do cut your speaker cables, it is best to cut them the same length. Though for short distances, again, this is not much of a problem.
I really don't consider cables of the length you have to be much of a problem. As far as closeness to power cables, if you can't hear a problem, then you probably don't have one.
Also, consider this, this wire is moderately expensive (£2.99/M) and you may not always have your speaker placed where they are now, so it might be wise to leave a little extra cable in case you move them. It's better to have wire and not need it, than to need it and not have it.
In general, unless you are experiencing a specific problem, I don't think you need to do anything except enjoy the music.
Steve/BlueWizard