What Joseph said. Get out the installation instructions and follow them. The reason people have issues is due to not following installation instructions and adhering to clearances.

I third on the read and follow the appliance install instructions. Also, curious about needing a strong material for large overhangs- you want to make sure you have a very strong support base for your countertop, regardless of the material it's made of. If your support is inadequate, even really strong materials can fail. Especially if you know it's on a very large overhang.

Millwork Man, thank you for your question. I would need to install countertop behind the range because it would be placed on a kitchen island, with 16 and 1/2 inches of counter depth behind it.

Thank you, Joseph, Vinmarks and Beesneeds, for the feedback to refer to clearances from the LG range manual. I should have mentioned in my post that I have not been able to get information from LG about clearances to combustible materials behind the range, at and below counter height. 

Their manual simply states, zero clearance to the wall, and wall coverings must be able to tolerate an ambient temperature of up to 196°. When I called technical support they only read from the manual, and even the supervisor could not give me clearance guidelines behind the range at, or below, counter height. 

I am attaching the clearance guidelines that LG lists in their manual, and linking their manual here: https://www.manua.ls/lg/lsgl6335f/manual

Technical support also told me the heat that is vented out of the range can be the same temperature of the heat in the oven, so way above 250°. I'm not sure if this is accurate information because it sounded like she was guessing. 

I would greatly appreciate any thoughts about whether quartz would be fine behind the range and whether I should use island trim, or something else to protect the quartz. (I would like to use Cambria if it seems appropriate for this application.) I wonder whether a different material such as quartzite or Dekton would hold up to the heat from the range vents, or if thermal shock over time would be a concern. Thank you again for your advice!

As long as the range back/sides areabove the counter height, (measurement D) it complies with the specs. The legs are adjustable, so adjust the whole to be about 1/4" above the counter height. And never use a pan larger than the burner, than hangs out over the counter. That will direct heat to the counter.

I have Taj Mahal quartzite slab backsplash behind an outdoor gas grill and it gets hit with high heat, grease and smoke. The Taj Mahal is doing fine, but it does get dirty really quickly due to grease and smoke. I also have a large vent hood over the grill.

Not all quartzites are the same, so buyer beware!

You do understand that heat expelled at the back of the range is routed through the black vent trim which is higher than the countertop behind the range, correct? The range is designed to be installed in a cutout whose countertop is 36" high. The vent trim is about 1" higher; heat does not come in direct contact with the countertop or anything below it.

That "Decor Guard" is not for this LSGL6335F range.

The heat coming out of these black vents on the top of the range is hot enough to give you a steam burn…

I assume the 16.5” overhang is for bar stools? Yikes! 😳 🥵😭

I believe that even a Quartz overhang cannot be more then 1/3 of the depth and no deeper then 15”. You can ask your contractor.

Sorry, I am no help on which countertop material would be best. If it matched your kitchen colors and style, the Taj Mahal recommended by Chipsa would be my choice.