Grounding the gate changes nothing.
There is no limiting resistor cause its a 12V LED. Its one of those you can swap with
the 12V halogen lamps in halogen systems: http://www.amazon.de/ersetzt-35Watt-Halogen-warmes-Kelvin/dp/B0076J5AHG/
They are really bright like 35Watt normal lamps and make a nice light.
The first LED i saw that really make sense when it comes to price<->power saving (amortization).
There is no CAT6 at the moment. Everything is short and on the breadboard 
But when you talk about shielding. Would you always connect the shield to ground?
Both ends ore just one?
I use just shielded cable:
Stranded CAT.5E SF/UTP for switches and flow sensors.
Stranded CAT.6 S/STP for network.
Solid CAT.6 S/FTP AWG23 for 12V power to the LEDs and Arduinos.
Lappkabel UNITRONIC LiYCY 2x0,25mm2 where i have to spread the 12V: Catalogue
And i want to make a extra cable from the breaker box to my home stereo.
I want to use Lappkabel ÖLFLEX 120 CH 3x2,5mm2: Catalogue
But i'm not sure what to to with the shield on this 220Volt cable.