Its academic TBH we had experimented with loads of manifolds in the day and we found the material was the key! Some stainless is too hard due to the compound material some used and the vibration caused cracking and splits over time. This is why there is as mentioned a flexi pipe to absorb any vibrations from the engine.
We finally decided that a stock cast iron mani reacted best with the resonated frequency from the block caused the least damage over time. As for performance wrapping the heat away from the engine bay made more difference than sticking an over sized manifold when the car didn’t need it at all!
The worst bunch was the Chrome ones they were just horriable to the core and reacted badly with resonated frequency. I'm guessing this is why most stock manifolds are cast iron?
