Lets look at this a little closer.
You have an engine failure over the mountains at 9000 feet and the tops of the mountains are 5000 feet.
Your average light airplane should have five minutes or more in the glide to allow you to choose a place somewhere down in a valley to land or crash land in.
Even if you wreck the airplane and you are injured you can still breathe and hopefully activate the ELT or maybe get on the radio to see if you can contact someone flying in the area.
If you land in the water your problem may be far worse for many reasons such as the ELT and radios will sink with the airplane and at best you will maybe have gotten out and inflated your raft.
At worse you will be bobbing around in the water slowly losing body temperature and your life expectancy will vary with the temperature of the water.
Will someone find you in time?
Also if you are injured or trapped in the airplane you be really out of luck.
Ever hit a big wave at flying speed?