This might give you some useful knowledge.......... https://www.sheldonbrown.com/calipers.html

Older info though. I don't think they mention direct mount. You definitely don't want those for your vintage bike. But again, I do recommend you get dual-pivot brakes if you are going to purchase another set. Depending on the manufacturer and what tier level prices can go from a few bucks to more than I'd want to pay. You can probably find a decent set front and back for less than $45.00 for the set. Might have to double check if they'll work with your brake levers though.

Hard to say how well any will feel for you stopping wise. That's a relative thing with respect to your experience and expectations. Also, rim material will make a big difference too. Chromed steel rims generally don't stop as well as will an aluminum rim with the same brake. And a 150 pound rider will stop a lot quicker than a 200 pound rider.

Generally with Shimano, as you go up through the tier levels you'll see that the more expensive tiers just look beefier and better. And they are. However any will be better for you than an old vintage brake that isn't working.