Gaia,
only you can decide what your comfortable with.
i have towed with a chevy cavalier that had no towing rating for 20,000 miles
pulling a 1500 pound atv/trailer combo. pulled like a dream,
used a subaru legacy for 45k miles, pulling same trailer no problems there either at 150k miles.
both were 4 cylinder automatic
there are people who live by numbers and people who actually try things to see if its in their comfort level.
as you have found out, people are doing it. those are really the only people to talk to since they really have experienced the towing situation
PS i never even installed a additional tranny cooler. although i did change the fluid on occasion
good luck
