Your local guy may not in fact actually be dressing the wheel at 5/8". That is a possibility. Is he honing/deburring the finished blade after it comes off the skate holder? How he does that step can make a difference, too. Finally, I wouldn't be surprised if your buddy an hour up the road is using a better quality finishing wheel than your local guy. That could be a factor in the difference you are feeling on ice. Too many unknown variables from one shop to the next at play here.
"The 3/4" feels sharper than the 5/8", with the benefit of increased glide. I've gotten a 5/8" from my buddy, and I had trouble stopping/felt like I was skating in sand. Way too much bite for me. " This makes sense from the difference when your buddy changes your hollow. Deeper hollow = more bite, blade sinks into ice more, less glide. Something doesn't add up from your local guy's set up though. JMHO.