We would have installed t-stat MB# 116 200 03 15 which is an 80deg C. The actual temp in an engine will always be 3-10 degs higher than your t-stat is rated at. The device starts opening at the temp its rated (actually I think it is rated at a partial opening at the quoted temp) and controls the bottom (min operating)temp from there on. The cooling capacity (of the system including the fan clutch)is responsible for keeping it cool from that point on.
Your car seems to be running at the right range for the t-stat you used. If it handlles the extra heat when it gets to 90 then you are OK. At around 100 or whenever the A/C gets working the additional fan will be added and help. I don't like to see the engines running above 100 even though MB says its OK.
The fan clutches very seldom fail and are a little pricey MB# 116 200 11 22 list $224.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician