Mainly because I scored a bunch of that Castrol Edge 5w-20 with Ti at the AZ sale. I've been running my 04 Accord K24 on 5w-30 for quite a while now, but in goes 5 qts. of the golden Castrol elixer! And "Oh, the Inhumanity!!!" Clacking valves, slapping pistons, screeching of bearings, I'll probably lose 5 mpg due to all the metal to metal contact going on in there!!! Once the oil heated up, I looked under the car to see the cascade of oil oozing past all my seals and gaskets! And you know... nothing... nothing at all was different. My butt dyno must be broken because for all the world the car drives and sounds exactly like it did on the 5w-30! So, either I'm imagining things about how 5w-30 makes my car quieter and smoother or the Castrol 5w-20 is one mighty fine oil! I think I've solved the thick vs. thin argument for myself, I'm gonna buy whatever's on sale! It's a good feeling to know it only cost me $5 to fill the pan with a top tier synthetic!!!