Relate this to Dunbar's Number and an effective small business. Dunbar says 150 total for a social group. But we operate across multiple social groups, across all realms of life, not just your job.
If you wanted to put together an elite group of excellent professionals, how big do you suspect that could be? In other words, how large should you let your company get before you spit it down the middle into two subsidiaries? My guess: 125
125 = 150 - (5 close family + 5 extended family + 4 close friends + 6 extended friends + 5 extracurricular friends)
Dunbar's number is the number of people in a group in which every individual knows every other individual personally. This is not the same as the number of people an individual can know personally.
The way you can split a company in two is identical to the way our brains already distinguish between social groups. I don't need to remember that John from work doesn't know Mary from the bridge club, only that there is no overlap between the two groups.
Another problem with the maximum company size that you propose is that Dunbar's number is not a hard limit of 150, it depends on the conditions under which such a group forms and operates. The Wikipedia article on it is, as so often, a good primer.
If you wanted to put together an elite group of excellent professionals, how big do you suspect that could be? In other words, how large should you let your company get before you spit it down the middle into two subsidiaries? My guess: 125
125 = 150 - (5 close family + 5 extended family + 4 close friends + 6 extended friends + 5 extracurricular friends)