Hard choice, really turning out to be neck and neck.
Arguably, the 4X6 is better for extreme trash, we are talking parking strips, around picnic tables, near structures. The 5.3 better for general searching... larger areas.
The augment comes in when you consider the 5.3 detection pattern comes to a fine point, perhaps better trash separation if a person knows how to lift the loop a bit to narrow the detection field pattern when needed. The 4X6 has the windshield wider effect... can also be manipulated when needed.
However, the 4X6 covers more ground at depth per pass, big advantage. That and I have dug small coins at 6 inches + with the 4X6, so depth is good.
Either way you can't go wrong for improved high trash use.
I still can not answer the question, "if you could only have one, which one"? Good thing I'm spoiled! I do tend to lean towards the 4X6 cause more ground coverage almost always translates to more finds and I have no problem pinpointing nor manipulating the "DD" detection pattern among multiple targets (angle, sweep direction, lift, and separate) .
Howard