Just wanted to bump up the thread with my story.

I decided to test this out myself.

Outside temp was 6degrees celcius
I drove about 30 minutes before doing the test, so it was on a warm motor. It started off at 71 then slowly climbed to 88-89 (took about 15 minutes of idling)

Then I drove onto the freeway for about 20 minutes with the cruise on 110km/h (68 mph)

The temps immediately dropped down to 70-71.
I just ordered a new t-stat, and so it'll probably get done sometime later this week. I'll update the thread again with my findings.

Current fuel mileage (according to my cluster) 8.6L/100 (~27.35 US MPG)
20" Nurburgring RF wheels