I just noticed from your pic that you are using v-brakes. I have never had a problem with stopping power using that style of brake. I can definitely make the bike lock wheels and skid. I can't imagine disk brakes being that much better.
Now on caliper brakes on my road bike, I actually have never been able to make that bike skid using the brakes.
I would consider disk brakes on the road bike.
just as a point of info, I am also a Clydesdale.
with that said, I would take the advice too just buy an alloy wheel set...