In the past I had always just added a couple inches to my shortboard for my step ups. My shortboards are 6'3" or 6'4 and my step ups would be 6'5"-6'6". Usually same width, maybe a little thicker and just a liter or two up in volume. This is fine for when I'm traveling, surfing point waves or reefs and when they get up in size I just add a couple inches and all is good. Here at home however I'm usually surfing imperfect beach breaks and with the added size come added current and a much larger playing field. In that scenario I've realized 2-3 extra inches really doesn't cut it.
This year I got a 6-10 Rusty Blackbird that's my normal width but a bit of a step up in thickness and overall volume (+1/4" and 7L). I love the thing. It makes me feel like I've kinda been blowing it all these years by pussyfooting around with stepup sizing. Despite being longer and thicker it doesn't require a change of approach to my surfing, really. It still pumps and turns and can be surfed aggressively, just with more control and confidence in larger surf. It's even fun in waves that are like head high if they have a little shape. I can still duckdive it fine.
I also got a 7-10 Pyzel Padillac this year but this one wasn't custom so it's both thicker and wider and the overall design is quite different from a "normal" step up. We haven't really had the waves for it but I've taken it out a few times just to get a feel for it and it's way more of an adjustment to ride. It's not that it can't be turned but it doesn't feel like something that I'll ever hit the lip with.