I'm going to drop this here again. The main thing to consider which I think most do, is the fact that oil becomes thinner with heat (viscosity lowers), but what I want to stress as @
Dezoris did was that you have to have the ideal weight of oil for the temps you will be running. Which I think most here understand but its good to re-emphasize. So when people give blanket statements saying 275F or 132C is safe they need to understand that yes the "oil" is fine but now you are risking your engine because the factory 0W-20's viscosity has dropped out of the engines optimal design range - I'm deducing this based on the weight of oil Subaru spec'd from factory. So looking at my link you can see the relationship of the different weights of oil vs temp. And from this you can make a better judgement if you should simply up the weight or run an oil cooler. The stock engine from reading everyone's UOA on stock oil seems to around ~7cST @ 100c so in saying that - our engines optimal protection range is from 5.6 to 9.3 cSt @ 100c based on the American petroleum institute website. Again, once temps start getting to 125-130 C with 0w-20 you are running your engine dangerously close to the fine edge of protection and could risk bearing damage when pushing it. In my post there is a link where you can input the oil that your thinking of running using its viscosity index and then click the temp range that you want the graph to start at ex) 95 degrees Celsius is a good starting point.
http://www.ft86club.com/forums/showthread.php?t=63955
I hope my post was clear as mud and can be useful to people. I've struggled with determining a good oil to run and have recently went through painstaking process of trying to educate myself on it and therefore make a better choice. In saying that I think I'm going to run Mobil 1 0W-20 again as I don't track my car and the highest temps I've seen are 120C while back roading and if during the summer it starts to get too hot I'll get the forester XT OEM cooler or run a thicker oil. Good luck.