Ahhh, there is not a proportional reduction in head loss, nor a proportional increase in heat transfer capacity over a 1/2' tube.
The heat transfer is all about wall surface area (and turbulence) and not the volume of liquid in the tube. Bigger is not always better. If it is 5/8 "nominal" meaning it says 5/8" on the box, it will be roughly 3/4" OD. The surface area for a 1/2" tube is 1.57 sq in/in of tube and for the 5/8" tube it is 1.96 sq in/in but volume is considerably higher ratio than that, 0.193 cu in for a 1/2" tube and 0.307 cu in/in for the 5.8" tube.....a very different ratio.
But this is not the big part. In any tube the majority of the liquid flows in the center of the tube and does not contribute to the heat transfer much. It does, however drop the head loss quite a bit, so you can use a longer tube without needing a bigger pump. The issue here is dT over the tube, the bigger it is, the less even the floor temp will be which is one reason why we try to design to a 20F dT.
The crimp rings are great because they are fast and relatively cheap, but not removable (without destroying them).
The pump pressure in entirely based on the resistance to flow due to the friction of the tube wall and fittings, weight of the water is not an issue.
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