OEM for the 08+ 4.7L is Bosch, I'm not sure about the older 4.7L. The reason you see many people saying 30k miles is because older years required that per the owner's manual. I would suggest you stick with oem plugs, they are a special plug (copper yttrium and iridium yttrium). Other plugs will most likely not perform as well and definitely will not last as long.
You can use the iridium one in the upper bank for longer life. I replaced my coils by need (rubber boot tears on removal of top bank). No need to though unless they fail. I believe now you can buy rubber boot replacements (couldn't when I needed them).
Yes dielectric electrical grease on the boot will help keep it from seizing. Just a dab of anti seize on the spark plug threads will also help keep from seizing into the head.
Also, if your boots are stuck to the plugs, take a piece of copper plumbing (can't remember if it's 3/8" or 1/2"), and cut a small section like 12" or 8" or so, and you can use that to separate the boot from the plug (after tearing the boot/coil off). Use a hammer to drive the copper tubing. The copper tubing will fit perfectly between the boot and the spark plug, then you can use needle nose pliers to pull the boot out.
I'll tell you I changed my top bank with the copper oem plug at around 50k miles I believe, then did both upper and lower banks with the iridium oem plug at around 110k miles, and the plugs looked really good both times. So you can definitely push them...
The only two reasons that makes sense are due to cost (would be more expensive for the owners). By using copper on the top they split the change intervals up and split the cost up (plus the coppers are cheaper). Otherwise, maybe due to the boot seizing the the plug issue? It'll probably be even worse going twice the miles.
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