Since Justin brought this up, we have had severalrams cold piston slap on 5w30, so much so that I wouldn't use it in cold state. At a minimum 0w30 redline, but 0w20 would be more aggresive.
Three choices, 0w20, 5w20, or 0w30. If you have hemi tick, 0w30 has proven to keep the tick just as quiet in trucks like hemi395's, but still better at piston slap. But it is a risk because that weight it is not as aggressive at cold piston slap. So if you compare the two 20 weights, you see a huge difference in cold performance and hot performance. 5w20 does better in hot viscosity tests noack and hths, and 0w20 kills it in cold performance. When you look at viscosity index, it is an easy choice man, 0w20 redline is the way to go if you need a 20 weight for that piston slap.
0w20 redline below...
Vis @ 100°C, CSt9.1
Vis @ 40°C, CSt48
Viscosity Index 172
CCS Viscosity, Poise, @ °C55@-35
Pour Point, °C-60
Pour Point, °F-76
NOACK Evaporation Loss,1hr @ 482°F (250°C), %9
HTHS Vis, CP @150°C, ASTM D4741 2.9
5w20 below...
Vis @ 100°C, CSt 9.0
Vis @ 40°C, CSt 53
Viscosity Index 147
CCS Viscosity, Poise, @ °C 60@-30
Pour Point, °C -45
Pour Point, °F -49
NOACK Evaporation Loss,1hr @ 482°F (250°C), % 8
HTHS Vis, CP @150°C, ASTM D4741 3.0