Send files to the other pane without dragging

Select items and press ⌃⇧⌘C to copy or ⌃⇧⌘M to move them into the folder shown in the other pane. Your focus and selection stay where they are.

How to do it

Open two panes side by side (View ▸ Pane Layout ▸ Side by Side).
In one pane, select the files or folders you want.
Press ⌃⇧⌘C to copy them, or ⌃⇧⌘M to move them, into the folder shown in the other pane.
Your selection and focus stay where they were, so you can keep going. If a name already exists, FileOctopus asks before replacing anything, and ⌘Z undoes the copy or move.
With three or more panes, right-click the selection and use Copy to Pane or Move to Pane to choose one.

⌃⇧⌘C⌃⇧⌘M