I'm currently in the process of buying my first driver suit to go endurance racing, and have found surprisingly little discussion out there about the ankle cuff design option. First is the traditional style, with just the little elastic cuff like the wrists have. Second is the 'boot cut' which adds a length of material beyond the elastic cuff that looks more like a traditional pant leg from the outside.
Of the few discussions about this that I've found, the vast majority of responses can be boiled down to one main claim. The suits both passed the same laboratory conditions certification testing, and therefore are equally safe. Therefore it's purely an aesthetic issue, and quipping that boot cut is for the NASCAR crowd.
There is also an argument against boot cut that appears to be fear of the (not loose enough to be floppy) boot portion getting caught on things and making it more difficult to get in/out of the car and of it getting in the way while driving... Although I don't recall seeing anybody who actually used a boot cut suit, even in formula cars with tight foot wells, who claim this being a problem for them.
The one argument in favor of boot cut that I've only come across once or twice is that the boot cut provides an extra layer of protection where the two pieces of safety equipment (suit and shoes) come together, especially since I've also seen some people mention their ankle cuff tending to work its way up over the course of a race.
There are a couple of things that jump to mind though that I haven't really found discussion on. First is that the suit testing does not appear to be performed in conjunction with other safety gear, to evaluate how the system works together at the joints between the items and not in (even simulated) real world conditions. So the system level protection is not necessarily equal.
The other is that the ankle cuff is effectively the same joint as the wrist cuff, except the driver having less ability to adjust it back into place during the race, and yet racing gloves do not stop at just barely overlapping only the elastic cuff. They are gauntlet style, extending beyond what would otherwise be the primary junction itself between the two pieces of gear.
As far as I can figure, the boot cut is basically doing for your ankles as the gauntlets are doing for your wrists. I don't think anybody believes that the gauntlets are really just an aesthetic decision, so why is that the discussion about the boot cut? Is it just that perhaps decades of experience has shown the foot well to be the last place typically innundated by fire, and by time it gets there the rest of the suit has already started exceeding it's protection limit anyways?