I think it really depends on the application. I had both, and found the 10x14 mono superior to the DD in performance ( depth, sensitivity, pin pointing) and weight, on salt water beaches.
But that is what I use my Infinium for.
If I were relic hunting or gold hunting in nasty dirt, then the DD may be the better coil.
Since 100% of the time I use my Infinium, I am beach hunting, I sold the DD coil.
It would be great if you could specify which coil you would want when you purchase an Infinium. I know first and foremost it's a gold hunting unit ( at least that is primarily what they are advertised as), the DD is the stock coil, but the Infinium is one hell of a beach machine once you learn how to tune it and get used to the sounds. For those who want to purchase one and use it for beach hunting, it would be nice if you could purchase it with the 10x14 mono or the 8 inch mono as the primary coil.