Converting 1 inch monoflow copper to Pex

[Al S]

I have a one inch monoflo trunk of copper that makes it way around the key areas of the basement that serves convectors via 1/2 pipe and the monoflo tees are on the supply side not the return side. The trunk is about 8 inches below the joists in the basement and I wanted to raise that trunk up to at least the faces of the joists. Since I am using PEX B (crimp connections), do I need to upsize to 1 1/4 PEX even though it feeds 1/2 inch tees. I guess the 1/2 inch pipe will be slightly smaller than the 1/2 inch copper. The flow will be obviously affected and my circulator pump is set to medium speed (default) for the copper circuit.

The questions then is: Has anyone made the switch? What were the lessons learned?

Thanks to all in advance
Al