Bro, he is using 20W50 and you're suggesting him to switch to 5W20 for his little turbo... you're not in his enemies, are you
5W30 and 10W30 will behave same at operation temperature. 5W30 would only flow fast when its needed to flow fast i.e. in cold start.
When electing an oil do care to take account of its API rating, ILSAC and OEM certifications... AND: what you want from your engine oil is lower pour point + higher flash point.
In general term: what you're looking for is the lowest first number and highest second one. (Not strictly true, but yeah; generally) Take Mobil-1 for an example: 5W50... probably the best engine oil to cite.
I'd suggest you to go for Castrol Magnatec if you want to stick with mineral, or Zic XQ if you want to go synthetic.