I had the demo bike for three days. It had 38 or 40mm Gravelkings on it. He set the bike up with relatively low pressure in the tires, which was great for gravel, but absolutely sucked on the road. I put more air in for a second ride, being careful not to overinflate, and immediately noticed the difference on the road, and didn't notice too much of a difference on gravel (not that I have enough experience to tell the difference - but I did notice a huge difference in how planted the Waheela, with wider tires, felt on gravel vs my road bike). But the GKs were rated at 50psi, a little more than half the psi of what I normally ride on the road. I am also setting up the road wheel set with a different cassette. 11-28 will do me just fine on the road.
I put about 60 miles on the bike over two days, at least a third of which was on gravel. On one of the routes I normally do on the road, there is about a hundred yard stretch of gravel to get from the road to the bike trail. It is a very slight decline with a slight bend. On the road bike, it is like walking on ice in flat-soled shoes, and the bike does not want to turn, even going maybe 5-8mph. On the Waheela, I was going down much steeper hills at 20mph (and applying the brakes to keep from going faster) and feeling planted.
