I'm pretty happy with 43mm Gravelking SK on the gravel around here, which can tend to be a bit rough. It also helps with things that might puncture a tire with a little less tread. I replaced one of my SK tires after it had dozens of punctures. It probably would have kept going. I have ridden 40mm Velocitas on smooth gravel, and it worked out fine. I have a GK SS that works okay, I bought it when there wasn't a lot of selection. Probably would have gotten the SK if it had been available.