In my mind when you want to choose your gearing, you think about climbing gears, cruising gears and overdrive gears. Your overdrive gear cannot be tall enough. If you make yourself aero and have the gonads, you can spin out a 55:11 = 5.0. So IMHO that’s the lowest priority.
For cruising, it depends on your fitness level to some degree, but if you are generous and set 45–50 km/h on a road bike, 38:10 = 42:11 is sufficient for that. The hour record for women was broken on a bike with a fixed gear of 58:14 = 4.14, i. e. easier than 42:10 and roughly equivalent to 50:12.
That leaves climbing gears. This is where you can cause or avoid a lot of suffering. I have never heard someone complain, because their climbing gear was too easy. Usually they had run out of climbing gears and were forced to grind along at 60 rpm.
Quoted for truth.
That’s why IMHO you should always prioritize having sufficiently easy climbing gears over having overdrive gears. Plus, it isn’t just about time: if you spin out at 55, 60 or 65 km/h, you are fast and you don’t have to do anything to stay fast. But if you are missing an easier gear and have to grind uphill, that’s … not fun.
I see so many people who are torturing themselves, because Shimano doesn’t believe in easier than 1-to-1 gearing on road bikes. You can get easier gearing, but you need to go beyond what Shimano officially supports. So most people I know do not do that, which is a pity. I think giving people proper gearing would make our sport more attractive to the masses.
If you are riding by yourself, sustaining 40+ km/h is possible for very fit amateurs, but even then all stars need to align — wind, terrain and you need to stay aero. In a group it is much easier. But even then you are talking about a group of fit individuals.
Plus, I’d reiterate a point from earlier: to make a gravel bike more versatile, you need to make some tradeoffs. On gravel tires, the cruising speed is lower because of the added rolling resistance. And likely, you want to climb steeper grades in slippier terrain, so you want lower gears.