I spend some time working out the math on various combinations of inner tubes and outer jackets. It's about midway down the page: Reference Materials
Area is in square inches:
CFC Configuration #1 3/8" OD Copper in 5/8" Hose
Wort Flow Cross Sectional Area 0.078
Coolant Flow Cross Sectional Area 0.196
Coolant to Wort Ratio 2.5
1/2" copper which is a typical supply to a hose bib is only 0.254 sq in of cross section so the coolant path in that CFC isn't much of a restriction.
On the other hand...
CFC Configuration #2 1/2" OD Copper in 5/8" Hose
Wort Flow Cross Sectional Area 0.149
Coolant Flow Cross Sectional Area 0.110
Coolant to Wort Ratio 0.7
I wouldn't be too happy with that design. It's going to flow the wort too fast in relationship to the coolant flow.