Comparing the loop in the air against the simple earth electrode (EE) antenna across the garden these are the results. Remember the loop could be improved by making it larger, using thicker wire and mounting it more fully vertical.
G4KPX - about 6dB better on loop
G6AVK - little difference
PA3ABK/2 - 1-3dB better on loop
G8HUH - little difference
M0PPP - copied on loop, no copy on EE
G3WCB - just copied on EE, no copy on loop
Conclusions? Well the loop, as it currently is arranged, is a bit better than the EE antenna by a few dB, in some directions, but not amazingly so. Will try a loop up in the air more in the coming weeks and we'll compare results again.