Agree. Rough rule of thumb is default 100 KB is good for 100 GB backup before it starts to slow due to having too many blocks to process. What exactly is “locally” in terms of storage type and transfer rate?
Increasing the Remote Volume Size talks about this, including how restores can slow when big remote volume size requires downloading multiple dblock files to gather needed blocks. Keeping it small would download better-tailored smaller dblock files, but more of them. It’s a tradeoff between access time and transfer time after access. Any local storage type that has a login might see the login add to the latency.