What I'm aiming for with the streaming is to try and help reduce latency. So if it takes 10 seconds to download a block and 20 to validate, it should take you 20 seconds total to do both. If it takes you 30 seconds to download and 10 to validate, then it should take you 30 seconds to do both.
Unless something weird has happened it takes ~no time anymore to validate a new block at the tip of the network its almost all already validated when you receive it.