Logically, yes that thicker oil will reduce that noise, but that oil is far from the recommended oil for the 2GR-FE. The recommended oil is 10W30 for most Australian conditions and I wouldn't want to go any thicker for the oil. You may be reducing the noise and having greater peace of mind, but you could also unknowingly be putting extra wear on your engine. Also, there has been some discussion over on the Aurion boards.
Piston Slap in Aurion
Rattle in start up
Hmmm Does not sounds right.
Your comment in relation to the 20S-50W and I quote "that oil is far from the recommended oil for the 2GR-FE" does not go along with what is "recommended" in the owners manual. I spoke to the technical division at Toyota and they confirm using 20W-50 can be used as per the manual. In the manual there is no reference of 10W-30 being the general recommended oil. Toyota technical division said to check the owners manual and based on the "mean temperature" that the vehicle drives in, then use the suggested oil accordingly. The 20W-50 lists as temps from -7C to 38C. Sounds like Australia to me.
I can not see how this 20W-50 oil could put extra wear on an engine? The fact that I am hearing piston slap, worries me more from an "Engine Wear" point of view. The idea of these metals behaving like this only brings up the thought of wearing in my mind! The clearances may be too big at cold. I have never seen this in a new car ever! The noise should NOT be there in the first place.
I have no doubt that my Aurion V6 engine runs like a dream since I put the Penrite 20W-50. Cold start noise is 80-90% less. The time taken for it to really smooth out is 2-3 minutes of driving instead of 10-15 minutes. I have gone from wanting to sell it to happy to keep it. (and by the way - I do not work for Penrite. They just make good oils)