You may have to separate users into tiers. For normies - 20 ppl per server is kind of a magic number for quite some time (but user density is gradually getting worse). For heavy users - sometimes 4 is too much. (I mean apps like Tableau and user consuming 4+ GB RAM). 64 bit Excel now is not capped to 2 GB per instance so Excel user may abuse the server (but that is for massive spreadsheets and macros etc.)