I have an 05 forester with a 2.5 n/a as my daily. The car sees a 15 min hwy drive almost everyday on my drive to a from work.  During that time I have a BlueDriver obd reader feeding live data to my phone. For the longest time, the car has stayed at a rock-solid 187 degrees during cruise at 60 mph. Yesterday I noticed that it climbed all the way to 210 before settling back down to 198. Coolant is full.  When I got out to feel the rad hoses, upper one was hot while lower one was stone cold. I’m thinking I have a sticking thermostat, but wanted a second opinion. Am I freaking out over nothing? 

Make sure you check the coolant in the radiator, when it's cold.  

Many times the coolant will not pull back into the radiator so the overflow bottle seems full but the coolant system is low.

Good visual of all hose connections, recommended.

Check to make sure all the fans are working.  

Is it an original Subaru thermostat?  Don't use and aftermarket.

Here are the specs on the thermostat from the FSM.

Starts to open:
Non-turbo model
80 — 84°C (176 — 183°F)
Turbo model
76 — 80°C (169 — 176°F)

Fully opens:
Non-turbo model
95°C (203°F)
Turbo model
91°C (196°F)

As Imdew said, make sure both fans run.

Coolant In the rad is full. Got an oem t stat in there that was put in about 16000 miles ago. Hoses are good and I will check the fans tomorrow. Thanks for the specs on the tstats Rampage