letting it spin down will be better for longevity (assuming you are using them alot, connected, minimal shutdowns) it would be bad, if you use those all the time, copy, spin down 10 min, copy again, etc etc.

but you might have other problems on your system if the powersave is losing 90% of your normal performance, are you running an index at the same time as your copy? you have to pause it while using your media.

t. the best way to get faster speeds is to avoid using w10. the bloat can affect transfers.