I've been working on an alternative cooking technique using the Egg, and had occasion to take non-contact measurements (with an IR thermometer) of a cast iron grate sitting on a drop-down spider.
With the dome temp at 550ºF, the temperature of the cast iron grate reads 750ºF. It's thus very easy to do a sear in a few seconds without using much lump; just move the meat closer to the lump. Not quite caveman style, but splitting the difference. It's possible that the temperature was even higher, but this was peaking out the range of my IR thermometer.
In this case, I had leftover Royal Oak lump that I stirred to let dust fall through. I then opened the vent fully. I lit in three places with torch, then put the (small) cast iron grate on top of the drop-down spider. I closed lid and left the DFMT off. Ten minutes later dome temperature was 550ºF, at which point I measured grate temp. This technique uses very little lump and I put no special effort into building a fire.
We have a general rule of thumb in the forum that dome temperature is 25ºF higher than grate temperature, decreasing as a cook progresses. I wonder if the 200ºF difference to drop-down spider temp is also generalizable.
My first attempt using this technique gave slightly overcooked meat. A 90-second-per side sear of precooked meat gave a sear that extended perhaps 1/8" into the meat, which was not what i wanted. Next time I will use a briefer sear, and perhaps a higher temp.