As far as I understand, to avoid too much heap pressure and read latency it is better to have the partition size within 100 MB. Also theoretically we can have 2B cell in a row but the practical size is to not go beyond 100k. same applies to a number of tombstones with in a partition by default because of the default tombstone threshold limit.
However why you are recommending 100k rows in a partition. Can't I have a 300k rows in a partition where my partition size is still 50 MB?