EQUP are the 4 electrode plugs with platinum center
EIX are a single electrode with super fine tip center.
E V-groved center electrode
I think i read somewhere that the plugs help with the smaller pulley and the more air going into the engine which is why the JCW comes with the colder plugs.
Colder plugs are better because you are increasing cylinder pressures and temps, the colder plug dissipates heat quicker from the center electrode, transferring that heat to the head, reducing pre-ignition. Its insurance against knocking to help keep the engine motoring longer
The performance benefits are debatable. Theory holds that at higher pressures, you need a smaller surface area of the electrodes to create a more concentrated spark as the fuel air mix gets more difficult to ignite. The theory behind the 4 electrode plug is that you provide more opportunity for the spark to jump depending on where the path of least resistance is through the air/fuel mix (and contrary to popular interwebs opinion, there is still only one spark, not four).
Just some anectotal evidence, a buddy of mine did some dyno runs at MC Racing in Merriam a few years back on his 944 Turbo and found no difference between Bosch 4 electrode and single electrode Platinums, and this is a car with nearly 300hp at the wheel. EQUP, EIX, or E for performance in our cars? dunno. What I do know is that my car runs great with either of the three.
Out on the open highway, I get 30 mpg w/cruise control at 74mph. In town, anywhere from 19-24, depending upon the leadfoot and whether I occassionally get it onto an interstate or just residential streets and urban stop & go. 
