With the RCM thermostat in place, we noticed that our car runs a lot cooler, when the AC fans kick on the coolant temp drops to as low as 175 degrees. Generally, the temperature dithers around 185 degrees and when really heat soaking in bumper-to-bumper traffic our temperature hit 203 degrees peak. We also noticed that the fans would kick on a lot less in general. When driving at highway speed the temperature ranges from 175-185 or 5-10 degrees cooler. So it seems like our peak temperatures were reduced by 6 degrees and the average temperatures in operation by 10 degrees. This might be a decent cooling advantage for track driving. As a note, if you have a stock radiator this mod is probably not worth it but it is probably something to consider when you have a high-capacity cooling system.
This thermostat comes with the rubber gasket and fits all Subaru EJ20, EJ22, and EJ25 engines.