I found trying compounds first was taking way too long.
So I tried using wet paper.
(very wet, used a bucket of water, repeated dipping and swishing off the paper plus splashing off the header, all to prevent a slurry buildup on the paper or metal of paper abrasive and what was coming off the metal)
400 for the initial knockdown, then 600, then compound with a rag.
Worked like a charm.