I don't really spend much time under cars other than oil changes any more because I haven't had to. The last time I spent more than 5 minutes under the car was to change replace a power steering cooling line on a friend of a friend's '94 Bonneville and that took a long time because I replaced it with an aftermarket part. The little old lady who owned the car didn't have the money to fix the car so I footed the bill for parts, and I didn't feel like spending over $500 for an OEM power steering cooler on someone else's 13 year old car.
5W-20 is probably OK to you in your car, but rather than obsess about it and start a long thread about something where we will never know a definitive answer and waste everyone's time, I'd just stick to what the factory said to use.