You need all the help you can get. The 3/4" manifold will cause less friction loss. What is the pressure at the meter and how long is the run. These things work together to create a viable system however a larger main coming from the meter would work much better to give you volume and more pressure when you turn on your faucets.I have a 1/2" water supply from the city. I'm redoing some plumbing fixtures in my home. Is there any reason to go with a 3/4" manifold?