Roundback vs. Squareback alternators?

Years ago when I was replacing alternators in customers cars, I asked my local rebuilder about the differences in the alternators. He basically said he could change the output on any of them and generally made them the highest he could with the parts that were available at the time. He'd also supply whatever output you wanted if you had a preference. Most of the rebuilds you get come with small diameter double groove pulleys which is good for most street applications. On race cars or engines that will see high rpm use, the larger diameter pulleys will allow the alt to live longer. That reminds me....I need to go see if he's still doing that work as I need one freshened up for a resto.