Deleting from the cursor to the end of the file is not something I do often enough to bind to make it worth binding to a single key. I’d do this:
- C-space (
set-mark) - M-> (
end-of-buffer) - C-w (
kill-region)
Just because it combines common actions and is therefore easy to remember.
There may be a sequence that uses fewer keys, but I prefer the simple.