We've debated this a lot: bell boots and polo wraps?? leg protection for barrel racing!???? Does my horse need protective boots Boots vs Polos .... Here is the Professional's Choice SMB study from 1998 ...
Basically, sport boots are going to be personal preference.
I myself prefer Professional's Choice SMB 3 boots on all four legs, plus Classic Equine Dyno-Turn bell boots on the front.
To me, I feel like Classic Equine are too bulky. There are some on here who love them.
I myself have not tried Iconoclast, but I personally feel like the double sling is redundant and a single sling is sufficient.
You really can't make a "wrong" choice between the boots you are debating. They are both good boots; just personal preference.