You gotta look close at the different spark plugs. There are platinum plugs and there are double platinum. The difference is that just platinum (aka single platinum) has a platinum cathode (tip) but just a regular iron ground lug. A double platinum has a platinum tip and a small platinum disc on the ground lug. A single platinum will last about twice as long as a copper core plug, 60k vs 30k. A double platinum will last 100k or more.
Iridium plugs can be single iridium, iridium tip and iron ground or iridium/platinum. Single iridium lasts about as long as a single platinum, about 60k. An iridium/platinum has an iridium tip and a platinum disc on the ground lug. They will last up to 120k. I have pulled iridium/platinum plugs at 120k and they show NO deterioration at all. They look like the've only been in for a week or two. Same for double platinums pulled at 100k.
Platinum tip provide a hotter spark than copper core plugs because the tip has a much smaller diameter. Size matters because the smaller the tip, the more concentrated the corona becomes just before it sparks, thus giving a hotter spark. Iridium has an ever smaller diameter tip so it has an even hotter spark. BTW Hotter spark has nothing to do with heat range. You want the correct heat range no matter what, that is the heat retained by the spark plug itself.
It has been my experience that performance coils do not last as long as stock coils. Performance coils use thinner wire to get more turns in the coils. More coils develop more voltage which tends to break down the insulation between the coils quicker. The issue there is that the smaller wires also have higher resistance so most of that extra voltage is dropped by the coil and not by the plugs. Once the plugs reach firing voltage, more voltage does not do anything. Also it is current in the spark and higher voltage, less current.
The reality is that once the fuel/air mixture starts to burn, the spark has does its job. More spark is just wasted. BUT, the reason for wanting a hotter spark in the first place is that as the fuel/air ratio deviates from ideal, it is harder to ignite. A weak spark can ignite an ideal F/A mix no problem but unfortunately, even with modern computer controlled fuel injection, F/A is not always ideal. The OEM plugs and oils are adequate for any F/A that a well maintained engine will have.
I'd recommend the direct replacement iridium/platinum plug if available, double platinum would be my second choice. Stay with the stock coils. Performance coils are for race vehicles that often see overly rich F/A ratios to get that last possible HP out of the engine. They need the hottest possible spark because some of those ratios are hard to ignite.
Now for something that will be a little controversial. DO NOT torque your plugs. This is from an engineering perspective. Engineers have found that percentage of compression or stretch as it is sometimes called gives the maximum sealing. You will hit the ideal compression using torque angle much better than using torque. Spark plug directions have always come with a torque value and an alternative method for those who don't own a torque wrench. People used to think that the torque was superior, but it turns out that isn't true.
If the spark plugs have a tapered seat and no gasket, then you go finger tight plus 1/8 turn. That puts the ideal stretch on te threads and compression on the seat to give the maximum sealing and holding power. If the plugs have a flat seat with a gasket, then it is finger tight and either 3/4 or 7/8 turn, see directions for that plug.
Also one reason for replacing plugs at a given interval, even if they are good is that some plugs will develop dissimilar metal corrosion in the threads and will become impossible to remove. Iron plugs in an aluminum head are bad about this. On a regular iron bodied plug, anti-seize can help prevent this. NGK and some other manufacturers have developed a plating for the plugs that is very good at preventing corrosion in the threads. Some of these coating do not play well with anti-seize so do not use anti-seize with these plugs. I have also found that the plugs can stay in the heads for a long time and still come out easily. BUT, I would not reuse these plugs, once removed, replace. Can't say for sure that reusing would be a problem but a plug that is stuck in a head is an expensive spark plug. I would not take the chance.
