What thermostat do you run in a G330E ?

As part of overhauling the cooling system with a new radiator (BEHR) , water pump, and hoses, I also decided to fit a new thermostat. The original was rated at 92 C. However, the dealer happened to have 87 C in stock and so I fitted one of these. Now the pointer on temperature gauge sits at 80 C, right in the middle of the 8. Which I think may be a little on the cool side ?

The thermostats are available in 79 C (tropical climate), 85 C, 87 C and 92 C.

I think there was a reason that MB went to 92 C as standard for the M103 engine - at least for Northern Europe - but can't remember what it was?

Too cold might promote engine sludging, but perhaps not with modern synthetic engine oils?