The question is about "multiple processes", your answer is about "multiple clients". It's not clear if the question is about multiple processes on multiple machines, or maybe about multiple processes within a single OS. What if the latter? I use
mpv with aggressive readahead; or I use vmtouch and vlc; and I use them for large media files I open via (slowish) NFS. It seems to me that within a single OS the filesystem cache runs reasonably well, also for NFS. I mean if (a part of) a file is in the cache because of one program, it's there for another program.