Smooth high grade tarmac is not a problem all that is required is say 6 weeks of gradually increasing time daily to build up callouses / promote skin growing faster pads of tissue.
I'm a big bloke, 90kg so if I can do it anyone can.
Loose small hard stuff is the painful issue, getting enough time to adapt your feet slowly is the problem for most people.
I have run 16 plus miles on all the surfaces around here just with the 'classic' 1.2mm but I am certifiable.
If I had the money I would certainly try the new 'Trek' model either version - 8mm might make all the difference on a partially stony mountain ultra.
Running exclusively fore or mid strike then applying that to ultras by engineering your shoes would probably make you much faster.
Pulling an old pair of trainers apart and paring down the heel before gluing back up has been done by some very quick ultra runners.