This is fun, or confusing, isn't it. The answer may be that a 006 is a satisfactory circulator. My assumptions: Your boiler is in a basement level. You are supplying heated water to baseboards on a 3rd floor. The vertical distance and piping between your boiler and the baseboards is 30'. The zone being supplied has 30' of baseboard. The piping to the 3rd level and in the baseboards is 3/4". For simplicity I'm assuming added equivalent pipe length of 10' due to elbows and other fittings. You have a primary loop from which the zone is supplied by a zone circulator. Hot water is being supplied at 180F. The baseboard is rated at 600 btu/ft at 4 gpm, or 18,000 btu total.
In this situation I would suggest that static pressure when the system is cold probably should be above 12 psi, perhaps 14 psi, due to the third level. I assume you have sufficient expansion capacity and when the system is at 180F the pressure may be about 25 psi. You have plenty of pressure to maintain hot water to the third level.
Pump head then is based on pipe length of 30' to reach the 3rd level + 30' of baseboard + 10' of equivalent pipe length = 70' total. Required flow is 4 gpm. Pump head of 70' of 3/4" pipe is about 4.5'.
Friction Loss Looking at the pump curve for a 006 at 4.5' of head the 006 will supply more than 4 gpm. You may need a circuit setter or other valve to reduce flow to 4 gpm.
This is an example. You may need to do your own research or consult with a professional for design of your actual system, or for selection of components for an existing system. I am not a professional, just a hobbyist, and I hope others spot any errors I might have made or can provide additional or more correct information.