Over water it doesn't matter because you are ditching anyway, so you don't need any kind of "decision height".
All you need is a few seconds' visibility of the surface so you can avoid flying into the front of a big wave.
But how will you fly at 6000 feet? On a "VFR" flight you may be illegal unless VMC on top can be assured, and on an IFR flight you will have a helluva fun getting a Eurocontrol route validated anywhere near that low down.
Also, not being a weather expert but hey I am now getting 85% on the mock JAA-crud IR Met exams, having done about 30 of them so I must know enough to fly an A330 through a CB or two
a warm front is not going to have
cloud tops at 4000ft. More like 24000ft, IME. 4000ft tops tend to be what you get with stratus between fronts, but the cloudbase won't be 500ft then, though it could be in the winter (with bad vis too).