I have the livernois tstat in my fusion. Temps usually will not go past 190 even in the warmer months. They actually drop if I floor it while entering the freeway or leaving a light. I'm guessing it's because of the increased flow.
Coolant shouldn't run lower than 195. You'll get accelerated wear in the engine. A 190 thermostat should be the limit. Set the fan to run around 198. Oil needs to get up passed 200 and should be around 220 to be optimal.
I've run the Reische 170F t-stat in the SHO and did several UOAs that didn't show anything bad. The 170F t-stat will keep the ECT as low as 180-183F in the winter time. It's important on the Fusion Sport because the coolant gets routed into the trans case and the PTU case. If you log Trans Fluid Temp, it never runs cooler than the ECT. I figure a Reische 170 would help the trans and PTU last a lot longer, but I don't feel like messing up the oil pan trying to support it while I remove the engine mount to access the t-stat.
Just an update on the Reische 170F t-stat I installed a couple of months ago. I, like Metro and his SHO, have found that my coolant temps have not exceeded 185 degrees while driving in the summer heat. Side note, my Unleashed 93 Tune, turns the fan on at 170 degrees.
I'm with metroplex, my '13 SHO was exactly the same way, but I installed it mostly as cheap insurance to the heat around here I live. In our Sports, given it helps cool our transmissions and PTU's, it's even more worth it to me as it's cheap insurance and overall longevity of the trans and PTU.