PEX monoflow versus two pipe on convectors

[Al S]

1955 ranch with monoflow feeding convectors. The 1-1/4" monoflow trunk is 6- 8 inches below the face of the joists in the basement. I want to consider raising the system to be tucked up closer and am considering replacing the copper with Uponor PEX. It's possible I need to replace the monoflow verturis with PEX monoflow tees.

Maybe a better option is to switch to a two pipe system and not use the monoflow tees. Is there a performance hit for this ?

Any advise greatly appreciated