It is like comparing apples and oranges, really.
I used the 13" Ultimate as my "daily" coil for the E-Trac. It separated as well as the Pro Coil and got, more or less, the same depth.
I use the 17" Smart Coil on the CTX for areas where trash is low to moderate, especially on sites with a lot of open ground. I would not use the 17" in some places where I would have used the E-Trac w/13" Ultimate like places with moderate to high trash.
Simply put, 17" Smart Coil is a specialty accessory that is great for wide-open and relatively low-trash sites (I mostly use it when I hunt Civil War camp and skirmish sites, which are now open fields).