All my solo rides right now are mixed surface- 40% road 60% gravel, and they have a decent amount of climb(40-70'/mile).
Recently I thought about breaking out a road bike and jumping on a flat bike trail that is also rural to see what I could pace on that. I actively try to avoid trails when riding solo, but that one is rural and an old rail line so its relatively low use and fairly flat. I have no idea what the difference in speed would be between gravel with some elevation and paved with little elevation, so kinda curious now. Just might need to give it a try.