Credit to the following information is from
Jeffrey Hurley at HS Tuning:
"We frequently get asked questions about spark plugs and ignition coils for MQB 2.0T cars, and I figured it might be helpful if I made a post to try to help mitigate confusion.
Current ignition coil revision: 06J 905 110 K
RS7 Plug, NGK version: 06K 905 601 M
Of course, both available at:
www.hstuning.com
Of course, the whole idea behind not using the stock plug found in your GTI, Golf R, A3, or S3 is that with higher pressures and temperatures, we benefit from a plug that's one heat range colder than stock. The stock spark plugs are a (7) heat range in NGK nomenclature, and one heat range colder is (8). Until now, we've had limited options to do so, as our plugs have some unique geometry. Many have used the 079 905 626 G or 079 905 626 M RS7 plugs which were manufactured by Beru. Because NGK is the world leading manufacturer or plugs and we've not once had an issue with their plugs, we tend to prefer them. We also appreciate that NGK is fairly open with information about their plugs, allowing us to make sure we're doing what is right for our engines.
If you look at the first picture I posted below, you'll notice some differences between the Denso IKH24 plug and the NGK RS7 plug. One of the most obvious differences is the terminal of the plug, where it meets with ignition coil. The Gen 3 TSI's have a conical spring connection at the spark plug rather than the traditional ball seat male/female terminal found on the IKH24. This was done because it saves length, allowing for a longer ceramic insulator. The longer insulator improves flashover resistance and the terminal cup shields the contact. The Denso plug has ribbing to cope with flash over, where the cup design on the NGK is meant to prevent it.
You'll also notice notice that the center electrode and the nose of the insulator are shaped a little differently between the two. The RS7 plug is much closer in shape to the original plug for the Gen 3 engines, the 06K 905 601 D. I'm still looking into the Denso geometry and whether it's a benefit, detriment, or neither. I'll report back if I can find anything definitive. This geometry mostly has to do with thermal conductivity and the path for dissipation of heat. It's mostly important though, that the firing end of the plug stay under 800 degrees C.
The NGK RS7 plug is a double Iridium plug, which means that the center electrode has a laser welded Iridium tip and the ground electrode has a square shaped Iridium coating. That means, that the interval on this plug should be closer to 35,000 miles (the RS7 interval), than the 15,000 or so with the IKH24, making it more cost effective in the long term. This is also good news for you water/meth users as Iridium is the most corrosion resistant metal on the planet, and very stable when exposed to methanol.
With regard to the ignition coils, they have gone through several revisions since the cars were released. The latest is manufactured by Borg Warner, a name we generally trust in the automotive world (DSG owners can thank them for that technology). So far, I've installed them in our GTI and monitored: knock, ignition, AFR, and torque for changes, and the newest coils do seem to be a slight improvement on the slightly aged components that were in the engine, but we are currently working on a test bench to provide more information. We did this for the MK5/MK6 owners and things worked out quite well for end users.
Because we now have a good double Iridium option, I see no reason to depart from the original design simply to have a plug that's one heat range colder than stock. We now have a plug that's made with the original features, by the best plug manufacturer in the world, in the correct heat range. I've paired them with the new coils in our GTI and have been happy with the results. Hopefully this clears up some things for you guys. I'm happy to answer any questions I can.
I also put together an ignition service kit with the newest coil revision and NGK RS7 plugs in case any of you are looking to refresh your parts. I also put the RS7 plugs up individually and as a pack of four if you just need to get the colder plugs in your engine.
Have a great weekend guys/girls!"