You are asking an irrelevent question for what you are doing. When you install two zones, each is controlled by its own zone valve. Therefore, what happens in one is independent of the other, regardless of any disparity in friction losses, flow rates, etc. In fact, one reason for two zones could be to separate the upper and lower floors of a multi-story house. In that case, the physics of the installation guarantee that there will be a disparity.
: My 70+ year old home has hot water heat, with all radiators on a single thermostat. I wish to break the heat distribution up to at least two zones. Plumbing and demolition/repair are not a real issue. I'm concerned with the compansation of pressure drops with pipe diameter in order to balance inter-zone heat distribution. Are there any "rules-of-thumb" or standard design practices in this effort?