Quick search shows George R R Martin wrote 3 to 4 million published words. ASOIAF is ~1.8 million. That's enough to focus on in my opinion.

Honestly, the amount of writing doesn't even seem that useful of a metric. Stephen king only wrote ~3x more than George, and about 6x more than someone like Nabakov (1.5 to 2 million words across two languages). The real takeaway IMO is to just write regardless of the technology you use

While he only did it, to my knowledge, for one book: Stephen King is the only major writer I have heard of to write a full novel with pen and paper (the novel in question was _Dreamcatcher_), which is really interesting to me.