I usually keep tax rates at 8.5% for R$; 9.0% for R$$; and 9.5% for R$$$. I still get overbuilding by R$$$. 10% for R$$$ seems to keep them down in numbers to a more reasonable amount, but you'll be constantly bombarded by the unfair tax rate message. I guess a city isn't supposed to be a "for profit" organization. But then seeing as Simland is a communist nation, does it really matter?