Would the 4x6 be better for gold, maybe?
Ans: probably not, unless you are hunting in high mineral ground or when the elliptical shape allows you to work the coil closer to the ground surface, such as when nugget hunting bedrock cracks or where the shape/size allows you to work in and around surface rocks in nugget country.
If you are referring to jewelry hunting the 5.3 coil has excellent sensitivity to small gold (chains and such) when attached to an MXT and it generally offers better discrimination at low disc settings as well. DD coils such as the 4x6 work better in high mineral ground of course but part of the reason they are made with an elliptical shape is to get back some of the sensitivity a DD loses on small gold when compared to a similar size concentric coil. Something that has to be kept in mind when discussing small gold is the difference between nugget hunting and jewelry hunting. Comparing small "nugget gold" and small "jewelry gold" is apples and oranges. With a detector like the MXT that will see sub grain size nuggets, finding small jewelry is an easy task regardless of the coil. Big or small DD or concentric they all work well when attached to the MXT for jewelry. As a general rule of thumb go with the better discrimination of the concentrics unless you prefer the increased ground coverage of the DD's or need to handle "tough" ground conditions.
Tom