1/2 loop and 3/4 loop. will this work?

I went to a customer the other day who has 3 zones with 3/4 basboard throughout the 3 floor house. The supply piping between baseboards is 1/2 piping. On the first floor he has 37.5 feet baseboard. (more than the 25 feet that can be supported by 1/2 pipe ) He says  that when temperatures are below 25 degrees.He can't get enough heat. He only wants to fix first floor this year.  Now I did  the heatloss calculations and he does need additional baseboard installed on the first floor. I wanted to put them in on their own 3/4 inch loop.Each zone has its own 007 pump. Here is my question: Will the fact that the 3/4 zones have less resistance than the 1/2 zones cause the rest of the zones not to heat properly? will the water not flow well through rest of 1/2 zones.?

Thanks

Joseph